Alright, enough is enough. I've been siting on this issue and just dealing with it for ages, but no, no more. 

As of Inferno and counting the Mezari, which for this purpose we have too, there are 13 factions with 6 heroes each. That's 70 heroes. Then there's the Haunt guy, the Sister of Mercy heroine, that guy from Frozen Fangs I don't have, 73. I'm 99% positive that faction quest heroes and that Broken Lord guy with the Ring of Unatural Hunter don't show up in the market under normal circumstances, but you can keep them in mind too. Duplicates of the vanilla heroes can and do show up too, so keep that in mind too.

Not all heroes are created equal. Some are clearly better than others for certain purposes, some are terrible for pretty much any purpose, and depending on your faction and goal, some are just completely useless. If you're not going to sea then stay far away from Mogwar leaders, Forgotten want nothing to do with Mage, Vaulter, and Mezari heroes both as governers and generals, Broken Lords cities governed by Necrophages might as well be leaderless, and so on.

And yet, and yet, even now, the hero market still only fits 10 fellows at a time.

This is not okay. Heroes are really, really important. You want them leading your armies, you want them governening your cities, they're important, but with every expansion it gets increasingly unlikely that you'll be able to get the sort of hero you want. I don't mean "Oh no I can't get Wayra Sigo in every game, waaaah," I'm not picky, I mean going to the market with the vaguest idea of what I'm looking for and coming up with absolutely nobody useful, every 15 turns, again and again and again. It's awful.

This needs to be fixed. I don't care if the other factions are in the same boat, it's not fun. If RNG doesn't like you, the entire hero mechanic might as well not exist for entire games, and that's not okay at all. 

Thoughts?

I agree.

As player in multi, we have identified this problem a long time ago.

You can have great difficulties to recruit a good industrial hero (Necrophages Slaver, Cultist), and it's an important nuisance.

There was a moment when we had a mod for multiplayer, this mod increased the hero pool from 8 heros to 10.

This kind of solution could be further improved, with a pool of 12 heroes for exemple. It's techniquely easy to do.

A more qualitative solution would be to reduce the frequence of the heroes not of your faction, and increase the frequence of your faction heros, as Exclusive heroes.

Another possible solution to the problem is to allow players to invest something to "cycle" the market. Maybe a research that allows a player to spend Dust (or some other resource) to shuffle the market and replace the current heroes with different heroes, or what not. It's not a great solution but it is an approach that can be taken. 

Yeah, I would also like to see the hero pool be expanded. With all the new hero additions, ten just isn't enough. Maybe expand the pool to 15 or 20?

I would also like to see at least one guaranteed hero from your faction. There are several faction quests that require the use of a hero fom your faction; and there is nothing more frustrating than getting stuck for 40 turns, because your required faction hero doesn't pop up in the market.

Have you tried the Endless Heroes mod in the workshop?