Regarding S2/S2-13, I personally think banning slot machines is stupid. I've actually tried attempting maxes via slot machines in S2, and it took me an average of 8 hours (and I believe some people discredited the charts because it was "easy to max" iirc). Additionally, it actually gets somewhat close between score grinding with perfect bonus (assuming its possible) vs. 999 with score grinding (because I was never left with too much time to do grinding anyways).
OK, I see the point.
Regarding SADX, those charts used to exist and actually still do (but you can't submit to them) if you know how to look. Personally I feel that's a bit of an iffy one. Comparing it to SA2 is not the same; SADX depends on ? boxes and SA2 does not, so it was easier to tell in SA2 just how many rings you dug up etc. With SADX, its entirely possible you can lose track and pick up additional ring(s) without knowing it, and due to the nature of random boxes, the world may never know.
Again, I see the point, but in SADX, despite the fact that there are ? ring boxes, there's still a rule: "Rings you dig up and collect as Knuckles don't count.". I should have mentioned that in the main post.
Regarding Heroes...well, that's 9 easy maxes (Chaotix CP requires you to get rings, and you already can't use the back ring for RA purposes). Chaotix CP I think has an easy max too, not sure. Additionally "banning slot machines" would be very hard to enforce considering you're controlling 3 members, not just one.
Oops... I guess I forgot what was CP objective for Chaotix and the fact, that your teammates can basically get rings for you in slot machines. It's probably because I hadn't played Sonic Heroes for quite a while now...
I don't have a strong opinion on SA boss ring/score charts either way. I don't really see an outstanding reason to deny them (but almost all charts would be easily maxable, since the 5k time bonus limit would be rigid in many cases, since that takes 1 minute to start dropping).
Look at e.g. Special charts for Sonic 1 (46 out of 72 players have max stats) and Rings charts for S3D (42 out of 83 players have max stats). They have easy maxable stats, yet they still exist.
About the scores; Chaos 0 would definetely be easily maxable, but Final Egg for Gamma is easily maxable too (51 out of 114 have max score) and it still exists. Perfect Chaos on the other hand would be pretty interesting (i guess) because of the fact, that your ring count keeps lowering and there's a limited supply of them too.
Re: Glitchless runs
What would be defined as a glitch? Let's start with that.
Well, I guess it depends on a game. In most of Genesis games (and their remakes perhaps) there are zips and slope glitch. As for Adventure games; continuously dying and hitting the same enemy to complete treasure hunting stages in ~5 seconds, while not a glitch, is a pretty big abuse of something the creators didn't probably notice.
Also, still in SADX: Tails Flight glitch (mainly in Speed Highway), Clipping glitches (mainly in Sonic's Casinopolis, Ice Cap and Lost World), Time Stop glitch (Sonic's Casinopolis and Twinkle Park), Jumping out of the rollercoaster (Sonic's Twinkle Park), Gravity glitch (Lost World), This: https://youtu.be/_4dGyB-loOA?t=9s
In SA2B:Clipping glitches, Sonic's Bounce glitch.
In Shadow: "infinite" Chaos Control glitch.
In Sonic '06: ... I guess the "High Jump Landing" glitch (Omega, Knuckles and Rouge: the glitch, where, when landing on ground the character is sent up high), no abusing of Purple Gem (Sonic), Silver's Air Dash glitch (the one, where he flies forwards farther than he's supposed to).
In SU360 and SG: M-Speed, D-Speed and Clipping glitch.
In most racing games: doing a lap without actually doing it (e.g. Sonic R - spiining in place near the begging), Respawn Glitch (All Stars Racing)
Those are just few examples, but in general: glitchless run would probably be considered a run, where you didn't purposely use any glitches that give you clear advantage.