I’m in the agree and disagree camp. 
The length of explanations can also get on my nerves, but I realize I do retain things a bit better if I take my time when learning to really read the explanations.
For me personally, it’s not like I’m expecting myself to remember a ten sentence menmonic like in your sheep example - but if I focussed on reading that blurb when learning the kanji/vocab, it gives me more possible methods of jarring the memory.
If I make my own, one-sentence mnemonic and tell myself to remember it whole: I have nothing to go on if I forget that short sentence. If I’m fuzzy on “Morally Good” and I read that menemonic well upon learning, I’m more likely to sit there going “Yeah, it was something about losing a horn. And finding a doctor? Because the sheep has no hands…? Hmm… A doctor… No! A morrally good doctor! Morrally good!”
It’s unfortunately quite impossible to make a learning system that is perfect for everyone, so perhaps the longer mnemonic system is less up your alley.
There is of course always the option of noting down any mnemonics that work better for you whenever you think of them. There is a user script that is no longer supported by the creator, and you might have to read through the thread for fixes if you have difficulty (I saw that Ad Block can interfere with it) but there is a user script that adds Kanji Damage Mnemonics. That way you can have other mnemonics to read through when learning that will possibly resonate more with you.
Good luck!