1/ phone tethering is the price to pay for end-to-end encryption: the support of multiple devices is not compatible with perfect forward secrecy, as the former require the asynchronous push of messages to all devices while PFS requires synchronicity (at least some kind of, as explained in their white paper here: https://lobste.rs/s/sx2f0r/whatsapp_encryption_overview_tech...
2/ if you don't like the Desktop App (or are using Linux), you can use https://web.whatsapp.com/ and/or the Chrome extension WhatsChrome https://chrome.google.com/webstore/detail/whatschrome/bgkodf...