I agree with your suggestion.
It would look more uniform to have 'Post' rounded, definitely.
Also, a rounded ring around the search area would make the top look uniform.
Further, a very thin cyan ring around the avatar would add to that uniform look.
The font also needs some modernizing. It is way too heavy. Specially on the dark theme.
Perhaps steemit should implement 'flavours' so that everyone can have their own look while keeping to the new look. Suddenly steemit is looking fresh and new.. a step in the right direction to appeal as an alternative to the standard.
Don't stop now though dev team. Innovation = admiration = adaptation.