You could of course mod the titan research to require up to 8 labs though... You are kind of right about titans entering the game very early though. Might be better to have the techt require 2-6 military labs. The dev's did playtest what was best for the game, so maybe when titans enter the battle during late stages of the game just makes them obsolete given the amount of resources they require to be built.

No one knows, titans will kill them to quickly with AoE abilities. Especially the Eradica, which arguably needs a debuff the most.

That is exactly what I'm getting at. If frigates are taken in isolation, we have a pretty good balance with the possible exception of carriers, and sadly we might never be able to fully balance their long range capacity. If corvettes could at least harass titans effectively, we'd have a much more dynamic game, as that would mean at the least you'd want some flak near your titan to counter the corvettes, and thus a possible opening for balanced fleets to return.

Fundamentally I don't think it matters where they put titans in the research tree, you could change it to be reasonable for whatever strength they have at lvl 1 while still a centerpiece ship at higher levels. As far as I'm concerned, 4 is a pretty decent place to put it.

If Titans come out later, they can be more powerful initially and not need to scale so heavily.  Hopefully that means Titans could be in a state where their losing levels and XP on death isn't an instant game-over for the player on the receiving end.

You could be right, but I don't know if such an option is on the table. The fact that they did not make titans lose a level on death when they adjusted the rebuild costs suggests to me that Starclad would really rather not implement that.

I agree with Greg that low level titans are not unreasonably difficult to take down, and hence are a welcome addition to mid game. Again unlike Experimental units in say Supreme Commander, they do not start out as unbeatable death machines and need to level up to get there. I think tier 4 is a good place that makes them not dominate early game while still giving you time to make good use of them in the second half of the game. You could make them start out as unbeatable death machines, but putting them at tier 8 and making them a lot more expensive would indeed lead to them being mostly unused in multiplayer except for clean up, which would be a shame in my opinion.