I appreciate your post, and in regards to that information I do not think the 1-50 "curve" on skill is correct. A Diamond 3 is not a "50" IMO. Competition/Skill wise, I would place that more around Onyx 1700. In regards to "veto", someone else already pointed out exactly why people want "veto" = We don't want to play gametypes/maps we dislike. It has nothing to do with playing the same map 2-3x, I will play The Pit on Halo 3 and Haven on Halo 4 all day long. You replied that you would rather remove/fix those gametypes/maps that are disliked, which is fine in theory, but 343 has not proven that they can do this in a timely manner. People raged so hard over Overgrowth/Riptide/Torque, frame rate issues with Pegasus/Orion, etc and they are all still in there. I don't think it's too much to ask that we (the paying customer), have SOME sort of input on what we are about to play for the next 12 minutes. If the majority of a lobby wants to veto for another option, so be it? It doesn't hurt anything, and it potentially saves people from quitting or being stuck on something they dislike.
Now for the ranks in general, here are some of my opinions from a longtime highly competitive Halo player. First off, there is very little incentive to even "get ranked". The reason people grinded so hard in H2/H3 was so they could show off their rank. In Halo 5, you grind your butt off for 2 months and then it disappears and you have absolutely nothing to show for it. Even something as simple as showing someone's "highest skill achieved" very large on the first page of their in-game service record would be a huge upgrade. The grand "reward" for playing ranked is an emblem that no one uses. I mean, seriously. I have recommended "XP" payouts, per rank, per season in a Reddit thread that had some very positive reviews. Instead of the emblem no one cares about, pay out XP per "rank". These would stack, so that after a 2 month season you could get a decent pay out. For example: Champion = 100k, Onyx 75k, Diamond 50k,etc. So if you end the season with 2 Onyx Ranks and a Diamond, you would get a nice 200k XP "reward". This provides a nice incentive for people to actually get rated in every playlist, and continue trying to rank up. It also helps with the ridiculous XP grind from 146-152.
As for matching itself, or why people in general don't want to play Arena...it goes without saying that randoms vs. TO4s is absolutely infuriating and it still blows my mind that this wasn't fixed before launch. It's also infuriating that you are given a rank, yet your "matching" is done by an invisible background rank. It makes the visible rank even more worthless. This has been a major complaint since Day 1. My background MMR has me in Onyx, but I get placed in Plat/Low Diamond, yet I continually face high Onyx/Champions. So from the start I am unfairly having to grind way too hard to get out of Platinum/Diamond to begin with. If my background says I am Onyx, put me in Onyx? Or if you are going to put me in Platinum, let me face Platinums and work my way out of it quickly so I can get to where I am supposed to be. I do not understand why Divisions can't face their own darn Division? What is the point of Divisions if you aren't going to pay any attention to that rank? Combine that with the fact that the matchmaking is designed to keep you at a 50% W/L ratio, it just isn't fun.
It's why people just want the 1-50 because it was so much simpler, and it wasn't designed to keep you at 50% w/l. If you were a level 40, you would face level 37-43ish. You wouldn't face a Level 50, unless you were rolling with a Level 50. According to your Halo 5 1-50+ comparison, I'm a Platinum 1 level 31, matching a level 60+ Champion. That is absolutely absurd, and would never happen in Halo 3 until you reached that rank.
All of this is too little, too late, in regards of saving Halo 5's Arena population, but I just hope all of this feedback helps with Halo 6. I've seen way too many friends leave Halo because of how frustrating the matching is, and how awful the ranking system is. Arena is miserable to me, a 12+ year die hard Halo veteran, I can only imagine how miserable it is for newcomers.