fraser1191 wrote:I mean barring deep strike an invuln and a 2+(which you can get in cover) aggressors are just shootier terminators with T5
They really aren't.
That's like saying barring deep strike, an invuln, and a 2+ Devastators are just Terminators with heavy weapons.
Aggressors are mobile rigs for support systems such as weapon rigs and jet packs. Terminators are tactical suits of armour that allows the user to perform assaults and precision strikes in a variety of battlefield situations. Both in rules and lore they can occupy quite different design space very easily.