Sometimes I have this problem too. Of course, there's a lot of people who will say, "You should probably switch mains," and this isn't ever going to stop. Even if they think you're the best Jigglypuff of all time, they'll still say you'll do much better with another character. I could bet enormous sums of money that even some great Jigglypuff mains like Seryneder and RDR7 have had this said to them too. And the thing is, they're probably right. I know that I would probably be better if I switched my main to a high/top tier, and I consider it a lot and get ready to tell people that I'm switching, but I never do.
This is because the reason why I play Jigglypuff is becuase I love exploring "different" characters, and getting sick rests, and getting sick edge guards, and getting sick reads, and getting sick combos, and just in general having fun. Jigglypuff is
tons of fun for me, and that's
why I play her, and that's
why I'll probably never switch to my secondary Peach or even a top tier as my main. Even through all the comments on my potential without her and all the losses against MUs that might be easy for a top/high tier, I still pull through. And it's because of this determination and hope and enjoyment I pull through.
However, it doesn't come without its stress! I'm very insecure about my results and image with Jigglypuff, and even though I have the skill to match a few of the better players in my locals, it's still very hard to compete with her sometimes. This is why I believe solo maining puff isn't a good idea. If the stress is too high of a factor, just push her back to a secondary or a pocket, or just stop.
In the end, it's your decision. If you have fun playing Jigglypuff, than keep it up! However, know this might limit you. If you want to become the best in general, than I suggest pushing her back a bit. There's still great players out there that keep Jigglypuff as a pocket/secondary! If she's no good, you don't have to play her. You might get caught in a "smash depression" switching mains/secondaries cause it will take time to get characters up to the level of your previous secondary/main, but it will be worth it in the end. If you want to keep maining puff, than keep doing that! It's not up to other players, only you. If you think you do better with other characters and want to play them, go ahead!