Keen flurry is only 8% average mitigation during its up-time.
Trading Bloodbath,Foresight....mercy stroke for that would be a mistake.

Heres something most don't consider.
Everyone is 190/7.5 on a base level (tank wise) using their Physical combos
25.33 tp per second.
When main tanking something that can be blocked, Shield swipe can change this for a PLD
Granted Drks also have (weaker) magical damage attacks that don't cost TP.

If Blood weapon is used off cooldown and no spells are used.
Drk is 26.3
A change as small as making Syphon strike 50 Tp puts the base expenditure of syphon strike combos to 24 tp a second.
55 tp would put the base expenditure of syphon strike combos to 24.6 (25.6 per second with blood weapon used on cooldown)

I'm not really sweating it because its a highly overexaggerated problem, but just reducing the TP cost of an action by 5 causes a notably large shift in TP expenditure of any job.

All this "Cross class lancer" stuff is garbage.