ugh...
your DM has no interest in the two sides of your gestalt being useful at the same time. This will be difficult to work around.
ok, this is my suggestion.
fighter1/rogue4/assassin4/rogue5-7/assassin5-9/rogue8-11//warlock9/hellfire warlock3/warlock10-17
Name your character kaboom, and just kaboom everything. 11d6 sneak attack, 14d6 eldritch blast, so 25d6 eldritch blast whilst invisible, and it can be a death attack. You're stuck with 3/4 BAB, therefore 3 attacks, means 75d6 damage/ round averaging 262.5 damage.
Ninja is probably just as good here, considering your stats.
This is consistant, even if your monster can see your invisible self, there are myriad ways to overcome this. Darkness him, chilling tentacle grapple him, find a way to blind him, hide in plain sight. Between the assassin spell list, and the warlock invocations, you should be pretty resourceful.
I don't know anything about MoI, but losing 1d6damage (10 damage/round) seems more than worth it for con healing. 3con/round is way too much to lose.
Regardless, there probably aren't very many things that can withstand 250 damage/round for more than 2 rounds, so I'm sure your party will love you.
Spell resistance will be a MAJOR issue for you, vitriolic blast every time if you must.
As far as I can tell this is the only way to really boost your effectiveness. Anything else that you could take would give you more
options, but not anything else. You could cast a spell
or eldritch blast them, but you could not do both. You could take a swing at them
or use an invocation, but not both. This build allows you to blast them and sneak attack them, and the limited spell lists of assassin and warlock can be arranged such that they would not overlap. Enjoy.
So before, when your DM said that you'd out-dps the party, it seems that he was only seeing half of the damage potential here. Show him this, ask him to change his mind about eldritch glaive so that you don't have to kaboom him.
The version of Divine Metamagic that I'm looking at says you apply it to "divine spells you know." So wouldn't that be only the Paladin spells that I could quicken, then?
from complete divine
Benefit: When you take this feat, choose a metamagic
feat. This feat applies only to that metamagic feat. As a free
action, you can take the energy from turning or rebuking
undead and use it to apply a metamagic feat to spells that
you know.