Makeb seems inordinately difficult

Yeah, I think that's the mirror to the pub quest.

IIRC, that's one of the last 2 or 3 missions in the Makeb storyline, so the OP is pretty close to finishing it. That said, the OP will DEFINITELY want to get geared up before taking on Archon.

Also, I agree that the mob density on Makeb is a tad too high. It's not that they're all that difficult to fight - it's that the density makes traveling much more time-consuming than on other planets. At least it does for me.

He said sentinel. Pub doesn't fight the Archon.

I know it has to be a gear issue since I'm still running around in outdated PvP gear, but I guess I'm just used to owning everything on my sent.

He said sentinel. Pub doesn't fight the Archon.

Two things: Gear up. Slow down. The level 52 through 54 crafted blue kit is cheap as chips on the GTN. Gear up yourself and your preferred companion and you will see a big difference. Also, Makeb is designed for you to level through at a certain pace. If you're 51 or 52 and fighting level 55 mobs, you need to go back and do the stuff you skipped in the lower level areas, or grind some low level dailies on the planet to catch up.

Unlike when you leveled from 1-50, every level you gain above 51 will send your stats further and further into the toilet, due to the punitive decreasing (not just diminishing) returns curve that Bioware imposed above level 50. If you do not upgrade your gear to counter the punitive stats nerf, then you'll have worse stats at 55 than you did at 45 (other than a bit more HP). That is why your performance seems to get worse and worse at an ever increasing rate as you level through Makeb, unless you upgrade to level 51+ gear. If you were in min / maxed Dread Guard, then you could probably make it to 55 without regearing, but WH / EWH is not going to cut it.

Yeah, they get "Glittering Fury", or whatever that pansy robot is called.
Probably a good thing in this case, you don't want to run into the Archon on a poorly geared character.