Well, as for Bitcoin, yeah it's true you can't add native BTC on Metamask/Rabby but there are wrapped versions of BTC on many L2s if Bitcoin is something you wanna hold or use in defi for example.
L1:s usually need another wallet. I was using Thorchain with the XDefi wallet but bridged my assets out of there cos the fees were too high and in my opinion, there are much better opportunities elsewhere. XDefi supporting LTC, BNB and BCH is a nice idea though.