This idea is only regarding m+ though its idea could be implimented into other areas of the game with thought.
The idea revolves around there being a measurement bar regarding a players actual skill level to go alongside base rio.
1) utilites
2) survival
What i would suggest would be that players get a base rio score for completing a key in time but also a star rating that accumilates for every key completed given by how well the player plays.
I did think perhaps there should be a rating for output but when i think about it this would not be needed so much as you need to also keep the system in place where the players who do not use utilities / survival AND do bad dps/healing can still get invited to keys. its the fundamental part of M+ to bring your own weight in output, the higher you go the more its obvious you did bring your own weight so for this judgement base rio score is enough.
1) utilities, i would suggest a system where overall in a dungeon you are rated by the game based on your utility usage, interupt usage of 70% should grant a 5* rating, this gives leeway for players holding there interupt for a specific spell. packs where there is nothing to interupt should not count towards the uptime. interupts still count when overlapped on a casting mob, not when a mob isnt casting to avoid manipulation.
Also extremely useful utilities like aoe stuns should be considered, these could even be intertwined into interupts as a buffer to reward well timed aoe stuns (waiting for multiple mobs to be casting) as a reward and a bonus addition to interupted mobs total rating. spells like knockbacks, ring of peace, silences could also buffer up the utilities rating.
2) survivability, a similar skill based rating system for survival and excecution of mechanics, taking failure damage hurts your star rating (not in a ridiculously unforgiving way as everyone makes mistakes) but i would say the number of times you take failure damage in a dungeon would need to be to quite a high standard as when you push in the biggest keys it gets more and more unforgiving. i would suggest a system of 3 or less times taking failure damage 5* 5 or less 4.5* 7 or less 4* etc. the balance has to be competitive to keep the ladder and all the players in the same kind of level of keys that they belong.
Another way to judge survivability is defensive usage. an uptime of 70% of big incoming damage would give 5* for example, another thing that is vital for pushing the highest level keys.
An even better way would be to have a flat rate amount of damage incoming for that level key and have the defensive usage / gear setup (shields/versa) determine the star rating.
Example being the bleed torment, that could be considered as a judgable incoming damage, if a mage iceblocks then all of that damage is avoided. 5* if he then eats all of the damage 2nd boss spires without using iceblock thats 2*, at the end of the dungeon all is calculated 3.5*
Buffers to survivability could be gained by using healpots within 3 seconds of taking a big hit (while pot is off cd)
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In a nutshell what this system would do would see players getting declined for keys due to there actual ability to play there class rather than base rio/ilvl/classviability. this would force them to go down in key levels in order to practice and learn the content to the point where there star rating for ability will improve.
Now what about new players that will be mega bad in the beginning and then be stuck with 2* rating? simple, have a hard reset every 4 weeks or so.
EVERYONE has something to work towards, shadowlands in my opinion hasnt been a massive failure due to the content, its due to the difficulty scaling with everyone able to complete the content insanely quickly and not having a reason to log in, "the alt friendly expansion" has really hurt the wow playerbase.
The players being bad at the game is not the problem, the problem with the game is there is no rating system or way to identify the best players or players that are good enough for that level, if you play m+ you know that if you miss the first weeks your basically screwed for the rest of the season, it doesnt matter how good you are, the only way you can climb the ladder is if you are lucky with pugs which is nothing more than a roll of the dice. joining endless pugs where the players arent good enough for the level is tedious to say the least. especially if your playing for 20 hours over a week in m+ and achieving zero score simply due to players that dont belong in that level key making new mistakes because they didnt learn yet.
This leads to a lot of unsubs in my opinion, players who play there class incredibly well but do not get rewarded for it watching on as new players who fail repeatidly in every key have more rio and go from group to group to group getting invites because there class is overpowered.
Bad players do not know they are bad, they think they are doing everything right, this kind of system would highlight that actually they need to go back to the drawing board and adjust there mindset if they want to push higher keys.
We have all seen it, your in a key and some ridiculously high rio player comes in makes loads of mistakes that cost the key and you find yourself asking "how the hell did he get that score" simple answer: he was lucky with groups. now with this system you would also be able to see his star ratings which would be low. it would give players a clear indication of a players general m+ ability, something that is vital for higher end keys.
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How would this effect the ladder system?
In every which way positive
The best players will be recognised with high star ratings thus invited to more groups, even if they were late to start you would see 1900 rio 5* 5* you could make a solid judgement based off this. check him out, oh he only started pushing this week and doesnt have any alternative week score. ask him the question "did you play previous expansions m+" he replies "yes i was world 5 in bfa". so your not obliviously declining top level players because they have no way to prove to you that they can play other than a blind rio score.
The bad players will get to see that there performance needs to improve to push higher keys and will play lower keys in order to practice/learn/increase there skill level.
Just a thought, give everyone something to play for. not just free handout 2500 rio to everyone who was born from his mother and decides to log in.
It would also combat the boosting issue at least in a small way.