I mentioned in my own post introducing myself that I had a nearly year-long Duolingo Japanese streak and nothing really to show for it, so I know how that feels! I know you explained you had a realisation that you really could understand Miku’s post, but I think lots of things in life can feel that way, and that’s normal. Everyone does everything at a different pace; lots of people never learn Japanese at all, much in the same way that I’ll never learn to play the flute!
I think part of the trick is not to compare yourself to others so much, as you touch on later. And when you do compare yourself, to interpret others’ progress and ability as a height to aspire to, rather than something to kick yourself about. When I see level 60 flairs around here, I never think “They’re so much better than me” - I usually think “wow, I’d love to be there too one day!”
Despite me complaining about Duolingo, it did actually teach me something. By complete chance, I met someone in my UK hometown on New Year’s Eve who’s spent the last 13 years living and working in Tokyo! After stumbling through a very short conversation, I managed to introduce myself in Japanese and even catch that he wanted to be friends with me (thank you vocabulary knowledge catching “tomodachi”)! Sometimes interactions like that can really remind you how connecting and amazing learning a language can be.