I actually think EV's made things more defensive. You can go 252 HP and 252 (Sp) Def, but you can't go 508 (Sp) Attk. Having the 252 cap on a stat means that while walls can invest in HP AND defenses to increase survivability, attackers can only pour so many EV's into an offensive stat and speed is usually an issue anyways. Even sweepers with priority (SD Luke, SD Scizor, and SD Quaza in Ubers) generally run 252 spe, albeit with a +Attk nature.
Well you never COULD go 508 (Sp) Atk. In GSC you were basically 252 in everything. Which meant that (all compared to third and 4th gen) 'sweepers' still had their maximum bulk, making them harder to take down, while 'walls' still had their maximum offenses, meaning that they could hit back harder while still walling effectively. Take Blissey as an example. Back in GSC it got 248 special attack, respectable for a wall. Now it's going to have less, or else reduce its walling ability.
Now the effects work against each other - GSC has harder-hitting walls and bulkier sweepers.
Let's take as an example, Blissey ice beaming Gengar. (It doesn't matter if this is unlikely in real battles.
GSC: Blissey 248 SpA, Gengar 323 HP, 248 SpD. Gengar takes 21-26%.
DPPt: Standard Wishbliss 206 SpA, standard Gengar 261 HP, 186 SpD. Gengar takes 29-34%.
So it seems that EVs ought to favour defense, but not in the way you implied. Rather, the defensive loss to sweepers outweighs the offensive loss to walls. But that's in the case of sweeper vs wall, and a wall that is attacking, not purely stalling while poison or weather damages. In the case of sweeper vs sweeper, things hit harder, and speed probably matters more.
I guess tanks are what are really hurt badly by EVs, since they want all their stats. For example Snorlax nowadays must compromise between offense and defense.
I've actually wondered if it would be possible to set up a cross-generations Shoddy server. All gens have their distinguishing features - RBY gets special joined, but fewest moves and can't hold items. GSC can max every stat. RSE and DPPt can push specific stats higher with natures. I'm not quite sure how to handle physical/special moves - possibly if DPPt Gyarados Waterfalls GSC Blissey, it uses Gyarados' Attack (because Waterfall is physical in DPPt) against Blissey's Special Defense (because Waterfall's special in GSC.) I think that would be really interesting, given you'd effectively have 1281 Pokemon.