I see what you're saying but by just having these orc characters, even though they are recycled from another game, still means they must belong to a race/faction that hasn't been fully established in the runebound series yet.
Orcs are very well established in the "runebound series" (meaning all of the other Terrinoth-based games.) They just aren't established as a Runewars "faction" (yet.) The potential for orcs to become a faction in Runewars is undeniable. Fans have certainly been demanding an orc (and a dwarf) faction - myself included, BTW - and FFG is historically quite good about responding to fan demand concerning their games.
I'm not trying to deny any of that, I'm just debating the idea that making an orc faction was somehow on FFG's books for this game from square one. I don't think their inclusion was an indication of any future plans for the game beyond the base box. I think it was an indication of their desire to reuse the same set of 12 sculpts they've been releasing in each base box set in the Terrinoth world, prior to DQ. Making an orc faction officially would be a response to fan demand, not something they had planned from the get-go.
As an aside, I'm rather glad they didn't include the same 12 sculpts in DQ. I'm sure they could easily have justified having 12 heroes to choose from in a 4 player game, given how random everything else in DQ is. However, I feel that the approach of having all new heroes in each game (potentially with cross-promotional hero sheets for the other games in the series) is a much better way to approach the whole "reusing the setting in multiple game lines" idea.
It's entirely possible that in the current Terrinoth universe that the Orcs are no longer a cohesive faction and are just a dying race that is interspersed throughout the land.
Indeed, this is more or less what the fluff from other games seemed to indicate. Orcs were a savage and tribal people who harrassed the Free Cities of Terrinoth, but when the Dragonlords invaded, the orcs recognized the greater threat and banded together with humans, elves, et al to repel these new oppressors. When the Dragon Wars were over, the orcs were effectively integrated into the Free Cities. They even held a significant population in the city of Dawnsmoor. There were still some savage orc tribes running loose, but most of the race was part of the Free Cities.
The creation of the Broken Plains faction in Rune Age is the first indication (in any of the Runebound games) that a significant, cohesive orcish faction exists outside of Terrinoth. Of course, Runewars did its share to redefine the political state of Terrinoth; making the Free Cities appear much more human-centric, where past games made them appear very multi-racial. It also established that the elves were a significant power in their own nation of Latari, and that their "near-extinction" in the Dragon Wars was apparently limited to those elves who lived in Terrinoth (either that or elves can breed like bunnies when they really need to.) In short, the world of Menarra is still very much evolving. Anything could happen.