Getting to the port before 11:30, you'll find a large crowd. Many people "just show up" around 10-10:30, regardless of their port arrival time. Since actual boarding doesn't begin until 11:30, the crowd just builds and builds until (generally) around 12:30 or so. The "sweet spot" for arrival is actually 12:15-12:45ish. That's after the mass of early arrivers and before the resort busses start arriving.
You won't "get on the boat earlier" just because you arrive at 10:00.
We've been on that first bus out from MCO. While the terminal is pretty empty when you first arrive, it gets to be a madhouse (not "relaxing" at all). There are limited seating options and people wind up trying to squeeze in anywhere they see 5 inches of space between people on the seats, or all over the floor (forget about getting up to stretch your legs - there'll be 5 people trying to sit in your now empty space). Then, once boarding begins, the masses just head for the line, regardless of their actual boarding number, and hover around the entrance to the queue "just waiting" for their number to be called. And, boy, do they love to give the stink-eye to anyone who says "excuse me, they've called my number" trying to get in the queue.
I've only embarked from Miami, but this checks out with my experience (though the crowding wasn't as bad as you describe--not sure if the Miami cruise terminal is bigger, if it's because I was boarding one of the smaller ships, or if it just happened to be a different vibe to the crowd). I'd ended up being among the first people there because the flight that was supposed to get me in the night before had been delayed and I'd ended up on a red-eye, so at 9:00 that morning I was looking at either sitting and waiting in the airport or sitting and waiting in the cruise terminal. Chose the cruise terminal. It was fine (I was able to find a seat at the far end, away from where people went up the escalator to board), but I sat and waited for
several hours before they even started boarding, plus I had a higher boarding number due to arriving by
DCL transfer and had to continue to wait a while after boarding had begun. I guess I got on the ship maybe an hour earlier than I would have if I'd arrived at 1:00, but I'm not sure I got even a full hour of extra ship time out of being there so early, and it meant that I didn't have anything to do while I waited but sit in my corner, watch the forklifts, and play around on my phone. 3/10 would not do it that way again.
We took the DCL bus from POR once. Yes, it left around noon. But they pick up your luggage from your room that morning, you just leave it in there packed with the tags on. (They did ours while we were at breakfast.) And when we got to the port there were no lines and we checked in and just walked right on the ship. It was the least stressful trip to the port that I have ever done.
Seriously, having done the early arrival to port once, it's
not what I envision when I envision a relaxing embarkation day--and that was coming direct from the Miami airport, not riding multiple buses (presumably ME to airport the night before, hotel shuttle to hotel the night before, hotel shuttle to airport that morning, DCL transfer to port--that's four bus rides when you could choose to do only one!) and handling one's own luggage through a lot of that. When I cruise in 2020 I'm going to have a slow, easy, relaxing morning at the resort. I'll have a leisurely breakfast while someone else deals with my luggage, then hang out by the pool until it's time to go.
That sounds really relaxing to me, even before we get to the part where I'll walk right on the ship within minutes of getting there.