I have experience from my toon, 104 Titan/102 Archer. Gear is good, almost top for PVE (+10 Bloody set, all epic jewels, shirts, cloak pve, authority circlets, 7s, abu, etc). Skills +10 both classes. Titan build for STR, Archer build for DEX. Dual skill static patk increase. The truth is that when mobs are close, Titan with spear hits more than 10 targets (maybe more in Altar or AF). Apart from my +12 3sa Bloody Slasher, i use Enhanced Shadow Pole for Titan, while Archer has +12 Dark Bow 7/8/Sigel. The pole and the bow could be comparable for PVE.
I think that Titan may be doing more dmg with spear when mobs are close, dps wise. If you know how to use Stun/Knock Down you help the party a lot too.
Of course stacked parties dont need more crowd control than the tank most of the time, they go for higher dps and kill rate. Also, no point comparing a fully stacked char with one that has normal gear. Thats why i compare my main and dual, cause they share gear, while each one has the best setup for the respective class and dual skills are shared.
From my experience, in Altar we go faster when the 4 DDs are Feoh, Yul, Tyrr/Evis, Dagger than when we have 2 Feohs and 2 Yuls. Of course that example does not include the case when top DDs are in party, so the 2 cases are not comparable.
So i guess the conclusion would be that if u have normal ppl in party with average or good gear (not top), the party benefits more from the variety os DDs, cause of the added stacked debuffs and the party solidarity, as well as the variety of dmg. If there is the possibility of changing this combination, i would do it only for adding a very stacked toon whose dmg would overcome all the above.