Yes. But Brad's argument is that Ashes didn't sell well because it was competing with older games in the same genre. If that's true, one would expect that to be true for games in other, related genres, too. Why buy Endless Space 2 when you could replay MOO2? Or why buy Endless Legend when you could just replay Alpha Centauri again or Master of Magic. Same argument, and I don't think it's valid at all.
But let's try to look at some numbers then using Steam Spy (no. of players), with a focus on recent RTS games, as well as a few re-releases (and while the numbers may not be exact, they should at least give some sort of indication of how well a particular game has sold):
* Original Ashes: 94,888 ± 8,547
* Ashes: Escalation: 18,534 ± 3,777
* Age of Empires II: 3,973,206 ± 55,019
* Age of Mythology: 1,028,658 ± 28,106
* Rise of Nations: 671,670 ± 22,722
* Wargame: AirLand Battle: 563,888 ± 20,822
* Wargame: Red Dragon: 512,516 ± 19,852
* 8-Bit Armies: 72,929 ± 7,493
* 8-Bit Hordes: 33,241 ± 5,059
* 8-Bit Invaders: 11,080 ± 2,921
* Act of Aggression Reboot: 124,704 ± 9,798
* Grey Goo: 300,378 ± 15,203
* Planetary Annihilation: Titans: 416,822 ± 17,906
I don't think it serves much purpose to compare your new game, with new IP, to re-releases of older games like Age of Empires. Those games do well, and that's largely because it's a large publisher and those games are well-loved, with people wanting to own those games on Steam.
So let's look at some original IPs. Based on these numbers, Ashes performed a little better than 8-Bit Armies. (Incidentally, the drop off from Ashes to Escalation is much bigger than from 8-Bit Armies to Hordes to Invaders, so there's an indication that people aren't as passionate about Ashes as about other games.) Compared to other original IPs, though, like Wargame, Grey Goo, and -- if you accept it as an original IP -- Act of Aggression, Ashes hasn't performed well at all. Grey Goo has three times as many players, and Wargame more than five times as many players. Even Planetary Annihilation: Titans, for all the crap it's been given by disgruntled people (obviously a vocal minority), has four times as many players.
Things get even more dramatic if you look at the stats for people playing in the past two weeks. Here are three examples:
* Ashes: 4,231 ± 1,804
* Escalation: 3,626 ± 1,671
* 8-Bit Armies: 6,447 ± 2,228
* Planetary Annihilation: Titans: 67,086 ± 7,187
* Grey Goo: 7,051 ± 2,330
Ashes is trailing well behind in that regard, too.
If Brad's argument was accurate, then games like Grey Goo and Wargame ought to have suffered, as well. But they seem to have done okay, and they're being played by plenty of people, even a fairly long time after release. So I would suggest the problem is not with Ashes's competition, with the game itself, which is fairly soulless (and perhaps that's why the technical aspects of the game were so hyped by Brad et al.).
Long story short, then. People didn't buy Ashes of the Singularity because they were spoiled for choice: they didn't buy it just didn't appeal to them. (And edit: I don't mean to be ragging on either Brad or Ashes, but I think framing Ashes's problems as something that's due to competitors is not a very constructive way of looking at things, and if anything recent attempts at fixing the single player experience certainly show that Stardock doesn't think the blame for Ashes not doing well should be shifted exclusively to people preferring to buy older or better known games over Ashes simply because they're older or better known.)