This is all opinion, I think front end could get by with just Javascript, but there is no way back end is going to get by with just Solidity.
Even if your entire focus is smart contract programming you are still going to spend a lot of your time calling/testing that contract from a language like Js or Py. It's not front end like React, but it's definitely not going to be all smart contracts.
In my opinion, you don't need to waste your time on web dev but you do need to be comfortable with a non contract language, and it can be anything as long as you can handle big numbers and make RPC requests.
Last opinion I would give, is that while one could use Solidity without knowing any Vyper or Huff (for example), good luck using Vyper or Huff without knowing some Solidity.
It's almost as true for knowing some Js in this space, even if only enough to be able to port aspects of an example or SDK (that will inevitable be released in Js first) over to your preferred language.