That's like saying side scrollers and turn based games are a relic of the past and should stay there because we have the technology to create beautiful 3D world and real time combat.
You'd be right man since it's how I worded it (wrongly that is), so, let me have another go :
Isometric view was a way as to have "bigger" worlds or, a "bigger field of view" of the game's world/levels/action on the screen at any given time using specific methods available at the time (ie, prerendered backgrounds and characters) since tech-wise, it couldn't be done differently (ie, full 3D/third person etc).
I understand that this method has cemented itself as a "game genre" (like 2D side scrollers that you also mention) but, always in my opinion, the isometric view is different since it feels that every game could have benefitted from a change to full 3D - imagine how cool, not to mention, (way) more atmospheric Diablo (and pretty much most dungeon crawler) games would be using a 3rd person camera - sure, you could argue that it would turn them into "simple" hack 'n' slashers but...isn't it what they are to begin with ?
I know, there's also sim building or strategy games that use the isometric camera so what could be done about them ? Well, that'd be an interesting question but I'm talking exclusively about isometric hack n slashers/action RPGs and the - now - ever cool rogue lites.
IMO - and I don't know if you played them - the Kingdom under fire games did it right back in the day, you'd have a zoomed out view of the action (which you could always zoom in) as to have stage awareness, as soon as you'd encounter an enemy army the action would switch to a full 3D, behind your back POV where the game basically turned into an even more badass version of Dynasty warriors (combos and all)
Again, I could understand the ISO camera for some strategy or sim building games but, I don't get why games like Hades or what have you have to use it.
Take the video in the 1st post for example, the game (Bloodborne) looses all of it's charm/atmosphere that way since You're losing all the atmospheric, extra details that the normal camera offers, it's like you're being the observer and not the... participant.
Hope it kind of makes sense but I can't put it into better words.
Cheers and sorry for the long post boys