Are classical players much weaker than blitz/rapid players? If yes, should I stop playing classical?

Classical is better than bullet, blitz or rapid. You should play at least 30+0 all the time, because that is REAL chess. Playing fast chess, like 1+0, is honestly just playing random moves. But I can't be talking, well, because I also play my portion of fast chess...

Play Classical for improving...Play Blitz and Bullet for fun

I believe the player pool in Classical is the smallest and weakest. I never played a single Classical game and I know some strong rapid and blitz players never played a single game too. If you enjoy playing Classical Time Control, keep playing. Other wise play Rapid time control.