Does making a new account make you worse at league?

Yes, you will pick up bad habits from playing low end games

I have to be honest with you, Once you get used to that level of plays, you will get quite a bit of losing streak after hopping back on your main, esp in ranked

If you can tolerate the enormous strength difference between your main & the newbies who always backs after being hit once, then it's up to you.

You will probably get matched with other smurfs, bringing your new friends into a very un-fun environment.

Yeah, I get matched up with other smurfs, and then I wind up feeding really hard, since I expect them all to suck.

Yeah, running into dem diamond level 5 smurfs aint fun. Nopenopenopenopenopenopenopenopenopenopenopenope

I mean, it's a weird question to answer, because the opposite is also true. Rather, what works on one level of play will not work in another, and you must adjust accordingly.

It's one of the issues of being in Silver. Other players believe they should be playing as if they were in Challenger, though the dynamics are so radically different that it can actually be detrimental to try (since they are of course only imitating, not understanding fully what they're doing, just that they think they should be doing it in some way and will frequently die trying things of which they have little to no understanding).

So...There's no clear yes or no, but you'll be adjusting.