Just an update in case any were interested (should probably move this thread I guess).

5 days later and it's a big difference. Badges are coming a lot easier now. There's 4 full dungeons I can clear (UK,OK,DTK,CoS) and from almost all the others I can get multiple bosses. I've made a number of Triumph badge purchases now swapping out the worst pieces of kit, next up is the i245 shoulders (need 50, currently have 37) which I'll get tomorrow night.

DPS is much improved now, as is tanks survivability.

I'm not (yet) blasting through each run in 15 minutes but certainly getting faster. Last run was H OK, cleared 4 bosses (all bar the cultist boss near the final boss - still working that one out) in 30 minutes for 4 Triumphs + 2 Frosts and no deaths.

Thanks again all for the helpful advice.