OG Ren it came down to:
Marathon servers were much less common. It was typically 45 min AOW servers.
This is why there was a lot of controversy with the community made patch for OG Ren that fixed the unbalanced points system (you could farm a lot of points using ramjet to shoot heavy armor tanks like mammy, similar to how VP farming with arty works).
Also it was common to purposely allow your most vulnerable building to die in order to prevent point farming. i.e. the Nod Ref on Under.
Time-To-Kill in OG Ren was significantly higher than in Ren X. This allowed for Ion/Nuke rushes, since it was a lot easier to cover an Ion/Nuke. Also I think the countdown timer was shorter?
APC + Tech/Hottie rush. You are right these were the most popular rushes. OG Ren APC driving dynamic is much simpler. In RenX it is much harder, you'll see people drive into each other trying to APC rush.
OG Ren doesn't have EMPs, AT mines or Silos, and of course no veterancy. Everything added in RenX that makes it easier to kill, also makes it easier to defend.
Back in Beta 3 when EMPs were added and they could be bought by any character (and before Commander powers), we regularly had 4 hour matches for several months until EMPs were nerfed. During that short period, tank rushes were nearly non-existent.
Also back in Beta3 when hotties/techs carried Carbines, it made inf-building kills very common. Hottie/tech was cheaper than the 1000chars and could kill just as fast if not faster.
I'd say #3 is most important. If APC handing is improved, the APC rushes will be back.