If we're talking about A ranks then yeah they could, especially if they got two members. Buffing it's HP so that it doesn't evaporate from level 80s is.. that's a HUGEEEEEEEEE hp difference. Went from a 5 minute fight (with ~2-3 people at level, which imo is very reasonable) to waste of your time unless you find the train. And SE has said these aren't meant to be 400 people monsters. To note some rank A have mechanics that make solo a lot more painful though.. lol, but I remember killing a few ~2 level higher than the NM (Rank A) early in HW and it didn't take very long (and when I had help it was much faster, and imo more fun than in the train (zerg is boring imo)). Also done it at level in small groups fairly quickly but I figured to mention solo'ing since you said it would take too long.
S ranks are a bit if we're talking about those though (not something you could small party at level). Like the FATE idea suggested for only S ranks, I think that could help get more people in on it though that comes at it's own issues.
Doesn't have to be what I want of course (obviously lol) but I'd love for something to change and I feel like at this point SE probably needs some change (because cross server killing is a bit ridiculous in terms of opportunity value, all the NMs multiple times over in a line if things go well XD).
I feel that the FATE change would be the simplest and fastest change but we already know that making them a FATE wont quell the issues entirely just a few minor points at the cost of some other new ones, I feel its like the placard fix for housing system- helpful and adds a different sort of stress but doesn't address the core problem (the issue made different/possibly lesser but many core problems still exist). Still, cheap and quick to implement is a commendable value to have lol.
Also FATE'ing only S ranks would still miss a lot of the points OP and others have bring up with the current hunt system. While I think rank S could work in FATE (though it sadly takes them off low party or high gear solo, which is kind of interesting thing to do) I don't think rank A should ever be considered for that as it would take them off the solo list for players and small at level groups who just happen to walk across one, which I feel like takes away some of that exciting open worldness of an NM. FATE'ing a rank S will in a some amount do that as well since before it could be a party of 55s or something but now that the boss balanced to 45 level 80's synced down so it's going to have some goliath god level hp. I guess I just see FATE as the way to pile way too many people into the room, promoting and exacerbating the other issues that people will have (and at a point making the FATE have trouble keeping up yet people will want it to be stronger every time lol) and is clearly (as they've said) not what people were meant to be doing with them (not that I think players HAVE to play the way SE intends, just that I think the system itself has a number of issues).
For the more classic hunt problems was why my suggestion was trying to create a split where the hunters (those who find monsters and spawn them) are rewarded more and have a bit of an intense race between each other while the NM killers (train/just want to kill big stuff in the open) / want the rewards can still come around in their little groups later and take part in the system too. While giving more of that "stumbling upon something" feeling (because you approach these epic remains and could potentially challenge them), protecting servers from being stripped (your little server, meet the balmung NM train lol), and give hunters basic info so trackers become less of "they killed it in secret hwo dare they, lets black list them"- if they missed the race one time they can join in the next time with the info the corpse gives them (rough in game timer support). But to address that people want old hunts (level 50 ones) to still be hard is why I thought we could perhaps get them to be bonfire'd (bonfire aesthetic if anyone remembers from Dark Souls), such that a group of level 80s could come up to the corpse of a rank S NM and revive them into something terrifying and maybe with new rewards. But you could change the bonfire style system into something more public if people really wanted like each week there was a new set of puzzle challenges. Llike how people had to figure out how to spawn S ranks, completing one gives you a new set with a slight time delay to promote many timezone benefits (up to a max # of super NMs a week). These taking you all over the place and once completed would allow you to go to the site of an NM (remains) and fill it with corrupted energy (perhaps lore wise there is too much void energy around so we use the NMs as a vessel to purge it). To make it more public feeling this method causes all the zones around it to ring and do a sort of reverberation effect on the screen for a few seconds, the zone with the NM gains a void weather (different Odin weather type) and after ~5-10 minutes it spawns ready to delete people (scaled to the current max level, amount of people in zone, and to the current highest non-savage ilvl at the time).