Don't get me wrong, unless you're doing black market slingshots, Mag and Predator armor milestones are significantly different when you have 1 scientist vs when you have 3, but that's pretty much the only hurdle. Engineers are still far more important considering they need to both staff and spelunk for income.
By the time it's time to go from t2->t3, the difference between 3 and 5 scientists isn't anywhere near as pronounced, and it really doesn't even matter anymore at that point anyway.
Maybe they also need a more reliable way to generate Intel the way Engineers generate supplies. Datapads seem to want to fulfill that role, except 1) it's too unpredictable/unreliable 2) it delays your teching, regardless if you have 1 scientist or 7 scientists, which generally relegates that method of Intel income to a luxury.
Fixing both these problems alongside giving them more things to staff would go a long way to making engineers vs scientists a little bit more of a debate. Tweak mission rewards to e.g. always give a couple Datapads, tone down the amount of intel per datapad and that will solve 1), Make datapad decryption a separate timeline that doesn't affect your research timer (heck, make it a laboratory staffing thing), bingo, solves 2)
