Passive is ‘having something done to’ you (or the subject).
ケーキが食べられた。The cake was eaten.
ケーキを食べられた。Somebody ate my cake (and I’m not happy about it).
〜てもらう is ‘having something done for’ you.
ケーキを食べてもらった Somebody ate my cake (and I’m happy about it).
i think curedolly is not referring to the actual verb もらう here, but tries to describe that (if you follow her logic) in japanese the subject is always acting. but in a sentence like „he was hit by the ball“ the subject is not acting, the ball is doing the hitting. therefore curedolly suggests another translation for japanese passive sentences that in contrast to the english version would translate „he was hit“ as „he received hitting“ or something like that. so the subject could still be the active part.
this receiving has nothing to do with もらう, this verb is active and the subject is acting.
i hope what i wrote is not confusing you even more … 
I feel like that’s overcomplicating things. The simplest reason we translate Japanese passive sentences into active sentences in English is just because the active voice is preferred in English. You can translate it as e.g. “was eaten” to make it passive and it works just fine. I think “the subject is always acting” is demonstrably false, since in a passive sentence like （私が）先生に怒られた, the agent is marked by に and the passive subject would still be marked with が (if it’s not omitted). もらう constructions are similar to the passive except that the action is being done on the subject’s behalf, rather than being done to the subject.
this is not my personal opinion, i tried to explain curedollys thoughts on japanese passive constructions. i dont know if you read her book unlocking japanese, but there she says that she considers the subject (marked with が) always as the doer of the action. and because of that she reinterprets the japanese construction we label as „passive“ as something different, where for example „receiving hitting“ is the action.
i’m not saying this is the best explanation, i just thought it would be useful as @_yasu explicitly referred to curedolly
I haven’t read curedolly’s book, but I’d need some good evidence to accept that claim. I’m going to put my reasoning for not liking that interpretation below. I decided to hide it in a summary block because it’s slightly off topic and I don’t want it to seem like it’s directed at you personally. If the curedolly explanation helps people then that’s cool. 
The passive voice is a grammatical construct that exists in many languages, and it always involves inverting the roles of the subject and object in relation to active sentences, so that the subject becomes the patient of the action and the object becomes the agent. Since we have a passive voice in English, I don’t see any reason to muddy one’s understanding by trying to contort passive sentences into strange constructions like “received hitting” when we have a perfectly functional passive voice “was hit” and furthermore a translation into the simple active where the object and subject are flipped is also perfectly understandable. (AがBに殴られた → B hit A; or A was hit by B). I’d be interested to see what kinds of arguments curedolly has for the Japanese passive voice not being a passive voice, but with what I understand I right now I see no reason to not view it as a passive voice.
CD agrees with you in that sense for those constructs that are actually passive. The distinction that she makes is when things like ケーキがたべたい are translated as “I want to eat cake.”
Her case, as @buburoi mentioned, is that it should be “The cake wanting-eating-does” and the original Japanese sentence isn’t a passive construction so it shouldn’t be taught as such.
I personally like CD’s explanations, but you have to go through her entire series to filter out the clickbait stuff and get to the meat of the argument.
For @_yasu:
Watch this video:
That’s her take on that construction and should provide more context for you.
I might be having a brain fart, but isn’t ケーキが食べた just “the cake ate”?
This isn’t to criticize you, but can you explain how she states that’s supposed to be more clear? That just makes it more confusing at least for me. If it works for some, that’s great, but that would simply make me more confused. 
田中さん: ケ—キはどこですか?
ヒロさん: ケ—キがたべた。
Eh, it’s a stretch but it’s illustrative of the point.
It really more applicable in something like ケ—キが食べたい but I don’t want to muddy the waters by bringing up the -たい form.
Edited to use a better example.
For me it fits my mental model better and I don’t know if that’s a product of growing up bilingual or the way I think in general. I’d much rather infer the meaning from the literal words than go straight to the meaning.
I’ll section off the rest since this is getting bit long for the “Short Grammar Questions” thread.
One of CD’s earliest videos goes over the fact that English is very ego-centric. The doer/subject/self usually has to be explicit.
In the cases where it’s not, that’s usually called the passive voice.
CD’s take is that 食べたい isn’t really “to want to eat”, it’s “wanting the action of eating” and in Japanese it’s perfectly fine for an inanimate object to do the “wanting the action of eating” even though it wouldn’t make sense in English.
But yeah, it’s not for everyone and it only makes sense if you go through all of her videos to understand what she’s getting at.
This means the cake ate. I’m not sure what point it is you’re referring to. It need to be 食べられた to be the cake was eaten.
Maybe not the greatest example. I usually avoid trying to explain the CD stuff because I don’t think I have enough chops yet to do it justice.
Let me edit and go with the -たい form instead.
The cake ate the chops, so we had to hunt it down and kill it.
一巻の終わりだ. 
This isn’t how Japanese monolingual dictionaries define what’s going on there, so I’m not sure if it’s just a theory pulled out of wherever. But it certainly isn’t how textbooks teach it, so it’s on brand.
But I don’t even see Japanese natives explain it this way. While this might be more “literal” in some sense (Edit: or maybe not based on Leebo’s post above), it just seems to be needlessly complex and roundabout way to teach something where a simpler English translation gets the idea across just as well.
I’ve watched about two dozen of her videos, so I’ve seen quite a bit of her system. I just don’t really see how that translation is any more clear. Oh well, not everything has to satisfy me so I’m glad it works for many.
Yeah she makes some of the mistakes she claims other people do by shoehorning some things in, but it’s internally consistent for the most part.
That’s probably where the divide lies. I find the other way more convoluted.
At the end of the day, you have use the things that work for you personally as long as the destination is the same.
@alo
I think you got thing completely mixed up because it’s nothing like what CD says about passive at all
カーキが食べた is not passive, it does not mean the cake eat-doing.
Edit:
This is not all how she frame things either. I have no idea where you get that 食べる is not “to eat” but “eating” and 食べたい “wanting the action of eating”, but it’s not in Cure Dolly.
That’s entirely possible. I’m trying to explain someone else’s method as far as I understand it so any mistakes are mine alone.
What’s convoluted about saying 食べる means “to eat”?
Probably the same thing that’s convoluted about わかる means “to understand”. But that’s just me.
I also like Common Core Math, so you can probably put me in the category with “those people”.