The Vasari rebel titan has an interesting concept with it's abilities. Basically it has a trigger ability that does a slow DMG/AM drain AOE DOT that has to be applied first before using it's large big hitting ability (and buff it's lvl6 ultimate as well). But both are rather short range, and originate from the center of the titan itself, so to be effective you really need to disable auto-casts, fly it into the middle of the enemy fleet, and set off a set of abilities in the proper order.
The challenge to that is that for a titan it really isn't all that resilient. At equal points into the game. (Titan is lvl6 at this point, while starting cap ship has reached 10 already) it only has just over twice the HP of the cap ship. Meanwhile the starbase has nearly twice the HP again as the titan, plus it's forward shield. The starbase also has significantly more raw damage output w/o requiring nearly the amount of micromanagement.
Here's the raw numbers for comparison. I'd post screen shots, but I don't want them to get taken down.
All numbers are with maximum research finished in all areas. All points available for spending went into raw offence/defense where applicable.
Hull: 27225, Shield: 13125, Armor: 36, Average DMG (all weapons): 692 [Incoming forward DMG reduced to 1/2 50% of the time]
Kultorask Titan (lvl6);
Hull: 9734, Shield: 12900, Armor: 23, Average DMG (all weapons): 576
Evacuator colony cap (lvl10);
Hull: 6515, Shield: 4079. Armor: 17, Average DMG (all weapons): 122
My starting capital ship hit lvl10 roughly about the time the titan hit lvl6, so I think it's a decently fair comparison point. Titan's usually seem to reach lvl8 about the time all 14 of your other capital's reach lvl10 for reference. That happen's quite slowly, and will still be a long time from when it hit lvl6, but once the rest of the capitals are lvl10 the titan will shoot from lvl8 to lvl10 quite rapidly.
On that note, since titan's take two capital ship slots, maybe I'd suggest that they earn two shares of XP instead of 1? (So with 1 titan and 1 capital the titan would get 66.7% and the capital would get 33.3% instead of 50/50, and with 1 titan and 14 capitals it would get 12.5% and each other capital would get 6.25%, instead of it and all 14 capital's each getting 6.7%) This would help quite a bit with your titan leveling insanely slowly when mixed with a large fleet, and allow it to hit lvl10 roughly at the same time as your other capitals.