It's not that Sword Base is 'too complicated', it's that it sucks to play in. It has terrible choke points, no flow, no easily identifiable areas, it looks terrible and you're forced to use a specific ability (jetpack) if you want to have a chance. The DMR and pistol suck not because you have to learn how to use them but because they provide zero feedback to the player and the blooming reticule is a worse mechanic than bullet spread. The idea behind spread or reticule bloom is to prevent one weapon from dominating across all gametypes. It doesn't work this way. Instead it creates an element of randomness and uncertainty that cheapens the satisfaction of getting a kill. It stops being a pure 1v1 battle and instead turns into a coin toss to see whether your reticule was .047 milliseconds smaller than the other guy.
The beauty of Halo's gameplay is that you start with similar weapons (BRs) and build strategies to get power weapons. It's as close to chess as you can get in a videogame. The mental battle you face when trying to decide when to push, grab rockets or OS, etc adds to the reward of becoming better and better at the game. I can see why people who don't play or suck at Halo like Reach because they can spam grenades and pick up the shiny purple gun and get kills. To me it feels like all the nuance is gone.