These really aren't the changes that Arbitration needed. It's unfortunate this is what D.E. came up with after acquiring 6 months of data.
Adding some form of revive is good. This is what arbitrations needed, because right now arbitration is severely limited in which frames you can run. There's two kinds of frames in arbitration: tanks and dead. So you have Inaros, Nidus, Gara, Rhino, Nezha... and the frames who are lucky to make it past 10 minutes.
Let's also keep in mind the fact that Warframe is, as a whole, still horribly unbalanced even after 6 years of development. Let's just say that having a permadeath mode when things like Toxic Ancients exist in their current form is purely ridiculous. Toxic Ancients: the things that walk up next to you and silently kill everything with no warning or counterplay. There's a hundred other examples...
Adding revives: good, thank you. Increasing enemy scaling: bad, and unnecessary. This is a traditional D.E. mistake: "We buffed something, therefore we must nerf something or increase difficulty. Because we operate from the assumption that this mode was already perfectly balanced so every buff requires a nerf, and every nerf requires a buff." Arbitrations weren't well-balanced, that's why you're changing them. No changes to level scaling were necessary.
Adding Arch-Gun rivens: good, thank you. It's great to add something new to the game, it's great to have rewards to bring people to play. This doesn't address the problems, and won't make people play arbitration.
The current state of arbitrations is this:
Tank-only meta: what I said.
PUGs don't work. People come in unprepared (trying to play a non-tank frame), and die. Frustrated, they usually swear off the mode. No one can blame them. Tanks survive, make it to 20 minutes or so then quit out of frustration.
Premade groups can make it to 40 minutes + (if everyone is playing a tank), but no one can stand to go past 40 minutes even if you're able to because the mode is a horrible, drawn-out slog and is not fun.
Arbitration mode takes too long, for too little rewards. Even in terms of grinding, even in terms of Warframe grinding, Arbitration takes too long, is too difficult, is not fun, and is unrewarding. You made the intervals in Arbitration missions take twice as long as normal, and that was a mistake. Bring it to parity with other modes in regard to the time to complete rounds/waves.
What I'd like to see in Arbitrations to fix it:
Add some form of revives (thus allowing non-tanks to be viable). Great change, keep it.
Decrease time for rewards to be on par with normal modes (people aren't playing because no one can stand to go for as long as is necessary. Too unrewarding for time invested.)
Do not increase rate of enemy level scaling. Unnecessary. Maxed out Tonkor barely kills things past 20-30 minutes. Why make ABCCC+ rotations when it's nigh-impossible to reach 40 minutes, and no one can stand to play it long enough to go past that? The math doesn't work.
Archgun rivens: Great, keep it. I'd love to get these, but it's not enough to make me play it really. Arbitration still isn't worth my time if reward intervals take twice as long while difficulty is ridiculous. Address the root problem.