Aggressors aren't the problem, they're just the symptom of the problem. The problem is 2W primaris and then all the free bonuses and offensive inflation they had to give out to make 2W primaris worth taking.
2W base troops are just problematic, because they're neither elite nor non-elite and that means the inflation necessary to make their elites appear elite compared to the 2W base troops is extreme.
You've still not shown how making the "tough" models have more wounds breaks the game. No one's arguing that the supplements weren't too much free stuff and hurt the game.
I'll go back to tyranid warriors, who have three(!) wounds and haven't destroyed the game. 2W marines gives the whole army (bar scouts, if they stay at 1W) an elite and durable slant, but that isn't a bad thing - it's what they're billed as.
It breaks expected unit capability against them, and makes engaging them less rewarding. This is much less of a problem with Tyranid Warriors because they are usually fielded alongside other units that are easer to kill, and Marine armies are far more common. Tyranid Warriors are generally taken in small enough amounts that you can afford to engage them with heavier weapons, leaving small arms to combat Gaunts, etc.
It's basically not that fun to have supposedly elite troops of other armies bounce off a swarm of Primaris infantry, and then have Primaris double-fire back with AP