The part about the visuals of the ships is mostly opinion. I don't think they're that ugly.

I mean... there are a lot of differences that separate Starfleet from the US Military. That seems like a bit much. However the militaristic thing in general is completely explained in universe. It's not just a "Oh, Starfleet is more of a military now!" thing. The Kelvin was rocking along, doing it's typical stuff, and then suddenly a massive warship with unheard of weaponry shows up and proceeds to obliterate it, killing a massive amount of people and forcing over 800 other people to run for their lives. All in no time at all and within Federation borders. Prime Timeline Starfleet beefed up the military aspect after the Borg and only increased due to the Dominion. Makes a lot of sense to me that they'd step up the militaristic aspect in a universe where a random incursion within their own borders left them completely defenseless. Then 20ish years later, the fleet that was sitting at Earth and is responsible for Earths defense is completely wiped out in less than 10 minutes by that same ship. At that point it would be absolutely idiotic to not have Starfleet be more militaristic.