Yes, and every single genre can be combined in a viable way. And games can be expanded to include other genres even if it hasn’t done so beforehand. We got after all games which work fantastic despite combining at first gaze very unfitting genre types… Rocket League being a prime example, soccer with cars is a little bit ‘special’ I would argue 
The same way goes with implementations. Path of Exile is a prime candidate for examples there as well, and a prime showcase on how H&S game design doesn’t have to be limited.
Not everyone for example likes rogue-lites, but the ‘Sanctum’ League implemented exactly that, in a good way too. Tower Defense with Blight, initially ‘city management’ style gameplay with Harvest (before massive changes as it flopped, but the idea was great) and more.
Do you think everyone liked those? Absolutely not… but there’s still a substantial sub-group of people which play those respective mechanics. Blight is well liked, Sanctum as well, both are as far away from the core-gameplay loop as it can be.
Now imagine EHG implementing one of those mechanics into LE, basically 1 to 1 in the style fitting for the game, with proper lore connections. Would you want to re-run 30+ minute lasting rogue-lite rounds for dozens or hundreds of times to acquire the specific loot you need which is only unique to this specific mechanic? Or would you enjoy playing a Tower-Defense for hours upon hours? How about needing to do both?
Well, the point is, in CoF without a supporting system to alleviate the demand to run those as a basically mandatory thing you’ll get many many unhappy people. There’s a reason why GGG provides ever further incentive to allow a comfortable SSF progression but… never saying it’s the ‘intended way to play’.
EHG outright made it so CoF is the intended way… but MG is also the intended way, so they need to make both work equally.
That means while providing the varied gameplay styles going along with several years long implementations it’s not allowed to piss of those which want to play CoF, hence acquire stuff on their own… while also not pissing those off playing MG, hence needing a functional economy.
The variance in content type will piss automatically people off if something meaningful is behind it that can be build defining, because then people need to engage with it despite hating it to progress their character. And if they don’t provide meaningful rewards at the end then you autmatically get ‘content bloat’ because those mechanics loose all meaning. Soulfire Bastion is a perfect showcase for that. It has nothing you don’t get somewhere else (outside the boss-uniques, which don’t drop always anyway) so it’s ‘worthless’ as soon as the content which provides it otherwise outpaces that.
Things like experimental affixes for example won’t ever become ‘meaningless’ no matter how long ago the mechanic is made, unless something taking the space of those affixes comes along. But exiled mages? Always great, always something to seek out. Bastion in comparison can be deleted simply and basically nobody would care.
The same goes for Arena. Outside of the boss-drop loot at the end it offers nothing. Hence nobody cares about it. Imagine it dropping unique loot solely acquired there between the waves and you got yourself a group of people suddenly playing it. Some saying ‘it’s their most enjoyed content’ suddenly while they’ve never even looked at it before that day with guarantee.
It’s extremely hard to implement mechanics and keep them ‘up to date’ when you have to balance some sort of baseline reward level whenever something new comes along. But when you got unique drops only available at that content… well… what are you comparing it against? There is no benchmark to decide ‘it’s not worth it’ or ‘it’s worth it’. People need the stuff and when it’s rare then people seek it out highly, if it’s common there then people will nonetheless run it to acquire it because it’s needed.
The game prepares you beforehand via the traps already present in the trials you need to finish to even access it. Also the traps are mitigated by defenses, they just do percentile damage, so EHP doesn’t mitigate it, you need to reduce the specific damage type instead.
It’s actually got a proper ramp-up and introduction phase for it. People don’t like it though because you’re enforced to run it as core progression is stuck behind it which you can’t trade for.
The exact thing which will happen in LE over time if it’s handled the same way… oh wait… welcome to Temporal Sanctum! Exactly 1 to 1 the same issue. People complain left and right that it’s a bother to do it, it’s annoying and not fun.
Nobody would complain if you get for example charges or a specific resource, you can sell that resource to others and hence aren’t mandated to do that type of content, instead allowing to do your personally favored type and acquire the resources through that in some way.
For MG as mentioned it’s selling that stuff and buying the other.
For CoF it would be the cross-drop mechanic as mentioned.
Because as you’ve properly said: ‘Everyone needs to do it’. But it doesn’t need to be ‘everyone’, it only needs to be ‘you’ and it needs to be ‘mandatory to progress’ in some way. The moment that happens it becomes not a choice but a chore.
It never will be. That’s an impossibility to implement. Dozens other games have tried, not a single one suceeded with that to date.
Personalities and flavors are too varied, there is no ‘unified’ enjoyment after all. So why try to enforce it when there’s options to not enforce it but still keep it meaningful… especially so given that letting that part be a choice will not only enhance the enjoyment for the player but also provide the option to be more creative with each separate mechanic?
Ohhh, that’s good to know. Exalted items are actually more valuable again. Though… I guess we won’t ever see exalted champion items properly anyway The chance for it to happen is just a tad bit low with the current item generation, unless we can actively generate that sealed affix in some way on an item. Which I doubt has been thought about.