Then do not do them. They are tuned to be finished with success with people that know how to play their spec good/optimally depending on key level. 2h Karazan is not really fun versus 30-40 min high paced high APM run.
The question is why? Because it was way above group capabilities? Was the DPS to low? To many people died? Healer could not keep up, tank was to slow with tempo? Bad strategy? M+ is the end game content, capable of replacing even mythic raids - not everyone will progress far on the key level.
“High” keys like +15 aren’t intended to be cleared successfully by every player. Even good players can just do a +15 not in time for the weekly because it’s that hard given week. This isn’t guaranteed content.
There is zero reasons to run Normal/HC/M0 dungeons… well M0 if you are really fresh with gearing a toon but that’s one week after which you outgear M0. Then slowly move over the M+ levels, if you don’t know given dungeon watch a video, try a low level run and so on. Not every run will succeed but that’s the nature of it.
Well either they are just to get a better run logged or you are trying key level way above your capabilities. Just log your run, upload to warcraftlogs, check your percentile parse, then go to wowanalyzer and check what it tells you about your efficiency. If you have grey/green parse then likely you can substantially improve your performance.
World quests quickly become obsolete. Although you have to do the invasions stuff if upgrading cloak from scratch… it has an end though.
Did a mage before 8.3 and it wasn’t that much interesting. Nearly end of the expansion and on low M+ key levels people still don’t know the basic mechanics. Like people don’t understand charm mechanic in Shrine and often they kill them self on the duo-boss, not to mention using interrupts. When good players do +15 bad players are challenged by a +6.
Also optimizing a DPS performance was quite “hard” and time consuming. Getting rotation ironed out (wowanalyzer is helpful), then trying to fish for correct azerite traits without which the DPS won’t get anywhere close to purple or even high blue parses… If you want to play a good DPS you have to main it and spend a lot of time at perfecting it. And you won’t be boosted in high M+/HC unless guildies offer that level of help (or you pay boosters). But then you get the gear and still have to spend lots of time getting most of your spec.
Right now much less people play, and those that do are mostly higher tier players doing more challenging content, like every +15 in time for the mount. Low level content is kind of dead so you didn’t get runs not because people don’t want you - just that there is less people and those that are playing are also more picky.
And if you are swapping characters then likely you miss a lot of performance on every. If you want to be really good at M+ 10-15 then you will have to focus on one character (or be a top 0.1% of best players maining more than one class/spec).