Halo was always based as an arena style shooter. Every person starts with the same weapons, the same attributes, and the same (balanced) spawn position that allows them to choose what they want to try to pickup in the beginning.
It gets thrown around a lot (to the point that it has lost a lot of the meaning) but Reach really did introduce the roll the dice / rock paper scisssors mechanic into Halo. This wasn't traditionally in the Halo playbook and it was too radical for a lot of the core group to stay with the series. Even the competitive leagues largely died off.
it was a revolutionary new look at what Halo could be and ultimately that gamble didn't pay off.
1. There are still playlists for that arean style play, so little to argue about here in my opinion.
2. That roll the dice mechanic actually still exists in the arena version too. Once the spawns are picked up and the first battles are out of the way your next encounter is very much chance and team communication about who, where, what etc. To me all loadouts do is speed this process up, to me it's evolutionary rather than revolutionary here and helps remove having to run, time or camp around fixed weapon spawns that can be farmed even.
3. I disagree, Reach was evolutionary. Look at the facts; very similar vehicles, weapons, strafe, jump, teamwork, map flows, choke points, power weapons not in loadouts, gametypes, playlists etc etc. In the end you may think arena vs. progression is vastly different but when you look at the evolution from CE, 2, 3 & Reach you can clearly see it as an iterative process and not a complete revolution.