Forgive this rambling, very tired and en route to bed.
As someone who's made it through Drexel, it can be done without major upgrades (but with the the add-ons you get from the Fleet Commendation vendor... specifically the power regulator that lets you put power to guns or shields, and the counter-measures that make you hard to hit.) It's still a rough run, but can be done, but it'll end up relying on strategy more than just tunnel-shooter skill:
I won't say it's easy, especially compared to the earlier Achenar incarnation of the same mission; even using this strategy only gets you through some of the time. Moreso with Tier 4, which makes it a lot less painful. But it CAN be done with Tier 3 and 4 mixed, albeit with some serious nail-biting moments. (My guild was treated to quite a bit of frustrated, dismayed remarks over Mumble when I first tried the mission...)