I'm not sure how much additional tiers would actually help. How far people are able to advance will always be dependent on the net change of arena points in the system. What additional tiers might do is reduce the point loss at the reset, particularly in G4 where the biggest drops will occur, but I don't know how many people are in G4 and how many of them make an effort to gain more arena points than they need to stay in G4 since platinum is basically a small whale playground that most people have no reason to try for. End of the day though, unless you have a net positive arena point change, there will always be people at the bottom no matter how long they've played or what teams they have, and that's not a great situation when we're talking about a feature that is important for your overall progress.
Regardless, if the goal is just to push people up, then bots/whatever is a perfectly fine solution, since they'll increase the generation of arena points. Is it satisfying to play? No, not really, but then I haven't felt any sort of satisfaction from playing the arena since my first month when there was some actual variety in teams (mostly on account of no one really knowing what they were doing, I suspect), before everything devolved into a speed race. In that sense, being able to progress while also not having to expend an effort in the arena is great. I've actually been using all my tokens recently. In addition, like I've said elsewhere, it's an enormous relief to escape from the power-based matchmaking system of bronze/silver which lets me do things elsewhere without getting punished for it. Still, the relief is somewhat blunted by that fear that at any point they might "fix" the arena again and I'll be screwed if I slip down to S4 again.
Actually fixing the arena to be something other than a comparison between luck on speed rolls for the most part would require a lot more work. If they aren't willing to do that, and I have seen nothing to indicate that they are, then making the arena something that people can for the most part ignore (with these supposed bots for example) is for the better. Having a feature that is irrelevant is far preferable to having a feature that is just frustrating.