you start thinking its a problem with you, and that maybe you're just not good enough or just not cut out for cubing
This is pretty much why I gave up on competitive speedcubing. I don't harbour hopes of becoming world-class, or even being competitive at local comps. Years of evidence point to those being impossible for me.
At least I still have fun cubing, and from time to time I randomly start breaking PBs and that feels great too.
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Re: learning "fancy" algs and whatnot.
At some point, learning something like full OLL and full PLL (or at least most of these) is the obviously correct choice if you want to improve. The marginal benefit from learning the worst cases is tiny, so, whatever, skip those for now if you want to; but 90% of the algs are worth learning and you're stunting your improvement by refusing to even start.
(Same goes for something like L2E on big cubes; besides the N perm cases which are just kinda bad, all of the other cases are very much worth learning and it perplexes me that some fast big cubers just… don't?)
However, when it comes to actually fancy alg sets (anything beyond standard OLL and PLL), there really are rapidly diminishing returns, and you shouldn't bother unless you've exhausted everything else you could improve on (this almost never happens) or if you don't care about optimal improvement and you want to try something fancy for the sake of it.
Large alg sets that cover individually rare situations will require correspondingly more practice to get fluent at; the threshold isn't that high for 2LLL (something like 100 solves per week, or even less? that's why I think 2LLL is worth it for most cubers), but for something like ZBLL you probably shouldn't bother unless you do 500+ solves per week.
Also, learning any one new thing is never going to
guarantee a certain amount of (short-term) improvement; there is a lot of individual variation. One person might find that full OLL made them (e.g.) 2 seconds faster, whereas someone else who had been using 2-look OLL for a very long time might instead find a much smaller improvement from learning full OLL, e.g. only half a second.