CO did a lot of things that blow CoH out of the water, stuff that the superhero genre absolutely needed.
Shame they built the entire thing on top of the corpse of CoH's design, both the bad AND the good.
CoH is a game that, in a lot of ways, didn't age well. There's a ton of stuff that feels incredibly dated, mostly because it IS dated (conventions that came out of more limited technology, mostly. Some design stuff, too, though). But the few things that did age well are things incredibly fundamental to making an MMO work properly. Such as allowing very easy mission coordination where everyone gets rewards, very easy team building and PUGing, especially once all the ATs were open to both sides, which fixed the cookie cutter trinity design blueside.
CO's regressive design on that front is one of the two big things that actually killed the game. People DO solo in MMOs. Frequently, even. But few people solo most of the time. And most players want to team up where possible. Especially if it increases XP! CO made coordinating this a dumpster fire, and any other games in the genre should be very careful to emulate CoH instead of CO in this regard. Honestly, almost all team based games should try and emulate CoH when it comes to this. Warframe, for instance, more or less uses similar design, and it puts a PUG matchmaking queue on top of it.
Back to the sad story of CO, though.. The other problem being the developer's complete and total obsession with nerfing, and the weird half baked design that was seen all across the powers and build systems.
The freeform system was terrific, but it became a bane of the game because people min maxing got so many things nerfed that pretty much everyone had to min max just to get an effective character. They did start to fix this eventually, but then they brought on a developer that fancied himself a WoW dev wannabe, who started nerfing again, designing really, really broken bosses (one shot damage everywhere) and was obsessed with emulating the endgame gear grind other games have (CoH developed this problem too, if I'm being fair, but they mitigated it better).
Blocking was a nice addition, but the way it worked was really clunky and half assed. It didn't stop crowd control, so the moment you let go you were instantly stunned. Enemies didn't experience blockstun or any kind of parried state, regardless of how well you timed it, so mechanically its functionality was flat. You can't "block and punish" enemy shtick attacks like you can in a proper action game. Block was functionally just a damage reduction that lasted as long as you held down the button. Bit underbaked.
There was a lot of stuff in the game like this, many powers and upgrades had interesting concepts that just didn't function well or were underpowered to the point of uselessness in practice. There are these little inklings that they wanted to better integrate travel powers into combat, the fact they used no energy and auto suppressed down to something comparable to running hover or combat jumping, so there was no need to switch between travel powers constantly, it was brilliant.
But they short changed what could be done with that, Superspeed had this interesting upgrade that was supposed to allow you to deliver more damage from an attack if it was executed after moving at high speed, but there was no meaningful system for building speed (it was all or nothing, like in CoH) and the ability didn't even seem to do anything (it probably did, but was so weak it was difficult to see what it was doing).
...I say all this to make a pretty basic point: The CoH relaunch seeing such success is one part legacy and nostalgia, and one part complete incompetency on the part of its competition. You can tell a similar story to the one here about CO for DCUO and probably any other bit competitor that came out.
Which I actually say to make another pretty basic point: There is a vacuum in the market to capitalize on here. Anyone who wanted to make a new Superhero MMO right now would be facing virtually no modern competition. Hint hint.
If Homecoming can snag the licence, and they have the talent to do it right, considering an actual CoH2 might not be a bad idea.