For instance, MetaMask supports Ethereum but not Solana, so users wanting access to Solana Web3 services would need a wallet like Solflare or Phantom.
Soon, your statement will be false due to Metamask Snaps feature. Basically it works like browser add-ons/extension in order to support blockchain not supported by MetaMask itself. I say soon since this feature is still on open beta.
What are your thoughts on this?
First of all, i would mention open source (or at least source code available) as one of many criteria of good web3 wallet. That means wallet such as bitget and Trust wallet are excluded by this criteria.