I've been experimenting with various characters to see if I can beat the various Heroic 4s around the world, partly just to see if there's anything interesting in the story and partly because I'm bored. I've come to the conclusion that some heroic 4s are absolutely impossible to solo at even level or even while they still give XP. You can be clever about stuff that requires you hitting switches or killing just a large number of mobs, but there's always some Heroic 4 that features like a guy with boss immunity and 3 elite friends that you cannot possibly solo unless you're 10 levels higher than the enemy.
Now people will say they're Heroic 4s, they're not meant to be soloed, and that's fine, but people pretty much never group up in this game to do anything. Besides, when you do beat them, the reward is usually something uninteresting like a random orange item with blue/green mix of parts, or 3 commendations. You won't get anything that makes you feel powerful even compared to just doing crew skills, and crew skills are weak right now. You get something like 2X worth of XP, except leveling is trivial in this game. Basically Heroic 4s only make sense if you know at least one other guys who likes to kill hordes of elites that are actually sort of challenging instead of just level up to 50 through normal quests and/or PvP. I mean, it's not like being able to duo a Heroic 4 teaches you any meaningful skill in the end game (well it actually does but if you can learn from that you're already set).
The Heroic 2s, on the other hand, are actually pretty well thought out. You can usually solo them if you really know what you're doing or you can grab some help, and it's not even clear if the Heroic 4s give better loot than the Heroic 2s.
There should be at most one Heroic 4 per planet, and Heroic 4s should give twice the reward compared to a Heroic 2 so that there might actually be a reason to try to find some other people to do them.
First, it's heroic 4, you need 4 people or 2 players with good control over the companions and well kept companions. I'll admit that for the most part when I get the heroic 2, 2+ and 4 quests, I untrack them because maybe I don't want to do them. However recently I've been seeing a lot of people asking in general for others doing those missions. That's usually when I join up and get them done.
I would expect to see that happen more often with the influx of F2P because they don't get rested xp but we may not. I'd suggest keeping an eye on the planets general channel when you are looking to do those. I do agree with your last statement though. The rewards from a heroic 4 should be significantly greater than that of a heroic 2 or 2+