If you sub anything but NIN on Tiamat you shouldn't be tanking it rofl. Especially with Mighty Strikes and double attacks, subbing RDM or lolWAR is like some bad 80s movie timewarp with messed up fashion sense and everyone is rapping hippity hop rofl.
It's pretty obvious that /RDM gives you more hate tools than /NIN but it's even more obvious PLD is fine with it's own hate tools and that you absolutely must negate the damage some way, like shadows. The only places that come to mind for subbing RDM is JoL, Ouryu and some kited fights.
You do realize how incredibly easy it is to cap VE as PLD? Sentinel -> Shield Bash -> Flash -> Cure4 and you're essentially there. What you didn't have cap is CE, because PLDs only CE is cures and flash.
Again, why in the world would you force upon a more difficult sub as a tank with no real benefits over NIN, that only MP sinks the entire fight for what? Slightly better hate in the first 5min? If the PLD/NIN couldn't get hate back, then he probably just sat there with full MP and only used flash without an HP macro or didn't bother to cure the lol/RDM getting mauled. Which was most likely the case if you couldn't cap CE.
I dont know how much you've fought Tiamat, but he's not news to us. We prefer not to spend more then 15-20 minutes tops on that fight. Hence we used PLD/RDM. As far as healing the socalled "PLD/RDM getting mauled", like i said, there wasnt much to cure. I understand your PLD's has far less gear then ours, but it shouldnt be to hard to understand that ppl with better gear takes less dmg. Blocked normal attacks hit for 0, blocked crit attacks for 50-ish. Normal attacks for about 100, and unblocked mighty strikes attacks for like 300. Where is the PLD getting mauled? even a double attack mighty strikes unblocked is only 600 dmg, wich isnt even close to being dangerous.
As for my own cures, this is what i was forced to use, since there was nothing to cure on Fygla.
input /equip ring1 "Bomb Queen Ring";
input /equip back "Gigant Mantle";
input /equip waist "Ocean Sash";
wait 5;
input /equip ring1 "Hercules' Ring";
input /equip back "Cerberus Mantle";
input /equip waist "Trance Belt";
And i spammed it nonstop between flashes, with a relic brd, refresh and parade gorget.
So like i said, if you cant even see how its feasible, you and your peeps must be gimp as shit.