Most of the problems listed are UI problems. You can use any client you want.
A few shortcomings of all current clients, particularly application clients (not web clients) are the inability to merge timelines, the inability to create custom timelines, the inability to follow instances and the inability to remote follow (client only follow, your account isn't actually following). These are all things technically possible that expand the usability of the software but nobody seems to implement it.
Beyond that, there's more than just mastodon there.
And the network can replace twitter. And it will, either it or something like it. Twitter is a company, it has to show revenue to investors, which means it has a limited lifespan hardcoded in. It has to change things, which always means alienating users. An open network like activitypub on the other hand, can function just fine with 2 users for a hundred years before people start using it. It doesn't have to have growth, which means it can continue on indefinitely. Nobody has to change anything, but you can if you want. Open tools will, in all cases, supplant the corporate offerings they compete with given enough time.