IIRC RA didn't actually use exactly the same engine as the original TD. I think the TD "Gold" (or GOTY?) edition ported TD to the engine of RA, which was slight

IIRC RA didn't actually use exactly the same engine as the original TD. I think the TD "Gold" (or GOTY?) edition ported TD to the engine of RA, which was slightly higher resolution and slightly prettier, so that's what most people think of when they think of TD. Whether TD and TD Gold were actually different engines I don't know but it must have been at least an improved version of the same engine. I think you're right that SC doomed TS to fail. SC was lauded for having three factions that are actually fundamentally different to a much greater degree than had been done before (e.g. Dune 2000) and had great storytelling compared to the well-done but low-budget and often cheesy narration in TD and RA. TS tried to one-up the genre with its cinematic cutscenes but they ended up creating an actual protagonist so the result felt much more like watching a movie than something you're actually involved in (especially when the protagonist does more than reacting and following orders -- which was the sole reason having a protagonist became necessary at all). Also, the engine was different and they tried to cash in on technological superiority with big talk of "voxels" but the end result just looked fuzzy and often sterile. They also tried to do the "multi-faction" thing by introducing the mutants (though not as a playable race) which confused the setting even more. TD was about futuristic modern warfare, TS was 100% sci-fi. In that sense I guess Generals was a bit of a return to the roots.