I understand and i've had a similar situation. Was in plat on main, got an alt that placed diamond with Lucio only but then I ranked up on my main. Imho the only reason why it happened for me and most likely this other person is confidence.

I thought I was stuck, got an alt and was playing more confidant, didn't care about losing and honestly it was great because it was pretty much stress free.

If you can be confident without needing to by another account then great but if you truly believe that you will benefit from it then go ahead, there's a sale on right now and they're pretty cheap. I'm saying I don't think it's needed.

Also maybe just get an alt anyway cause you could use it to learn new heroes.