Solidity is only important if you want to make dapps on Ethereum. Let's just say that most "dapps" are filling in ERC20 or ERC721 templates, so it's not exactly rocket science. My prediction is that the usefulness of ETH smart contracts will be less and less important over time.
I would recommend reading Mastering Bitcoin by Andreas or my upcoming book. You can also take my class programmingblockchain.com.