I've managed to craft a build I actually can compete for the middle of the scoreboard with on Platinum! I'm starting to like Geth Trooper. It is indeed tanky even with HM. Dunno why it's easier for me to survive with GT now on Plat than a month ago on Gold. Probably because I'm not trying to use flamer.
Funny thing is, I only put Arc Pistol here because I was going for its challenge, but I'm starting to like it, too (tried it and didn't like before). I even switched from AR amp to pistol amp, I prefer Arc Pistol for long range and for killing big bosses that are easy to hit in the head (Brutes, Ravagers, Scions, Praetorians).
The next improvement would be to replace Stronghold Package with AR or Pistol amp equipment. I think the benefit of Stronghold package is almost non-existent. Took it for even lower shield recharge delay.
P. S. Of the [few] map / faction combinations I've played so far, I found London / Collectors to be the easiest. I played a couple preset Reaper games as suggested earlier in this thread, but to hell with Banshees. There's too many of them, they tend to sneak up and hug me, and I can't hit them very well, esp. if there's more than one near me.