That's true, but don't forget that OP used an imaginary scenario in which they have 15 different cryptocurrencies. You have covered bitcoin and ethereum with Electrum and MetaMask, but what about the rest?
I do not know much about this, but I saw a Trezor article which is related to it and which may be helpful:
https://trezor.io/learn/a/third-party-apps-and-trezorWallets listed are Electrum, Exodus, MetaMast, MyEtherWallet and MyCrypto wallet. I do not know if MyCrypto wallet support many other coins because I have not used the wallet before. The last time I downloaded Exodus, it is supporting many cryptocurrencies including Solana and NFTs.