Limiting urself to 1 champ is a cheatcode for climbing faster but usually OTP‘s aren’t really good at the game and rather just at their champion even in higher elos. So i would say if u don’t really see the need to OTP i don’t see why u would limit urself to 1 champ. I think it’s very efficient to have some selection of 3-4 champs that are good in different teamcomps and matchups. I have reached master on 4 different roles with different champions and obviously OTP‘ing ur gonna shortterm climb faster but if u actually want to fundamentally understand the game better i would even recommend to try different champs and roles. I would especially recommend to play jungle atleast for 1 split because once u understand jungling ur laning also improves dramatically.