@Kyrt, regarding suppression of weapons: why can't you just look at the number of blast markers you have and then reduce the number of shots you can take based on that?
I agree that reducing firepower via DC could work just as well; the difference is really whether shooting at titans or damaging titans should suppress them. I don't think that particular weapons need to be knocked out; for simplicity, I would keep the choice up to the titan player (it could be handwaved as on-the-spot repairs, etc.).
@IKW Wartrader might be right with 2 BMs per suppressed weapon (though a speed penalty could be appropriate, too, but the simplest option is to just reduce firepower, like with every other suppressible formation in the game).
Now, onto the digression!
Splitting fire or activating separately are indeed not the solution for small titans. However, for large titans (Imperators and friends, and maybe down to Warlords) with large weapons loadouts, I'm not sure if they'd ever be balanced well (unless everyone plays with them for a while!) without split fire. Their large firepower can arbitrarily destroy most formations but since they can only focus on one formation at a time—excepting barrage overlap—the damage overflow can be quite significant if the enemy only has small formations. How does one balance that well (this isn't meant to be a patronising question! Just an honest observation)? How many points is a 'delete one unit' weapon worth? EA (and almost any wargame; see WH40K for current poor pricing!) pricing relies on how much damage a formation can do and that needs formations sitting in a regime where their firepower is not enough to destroy the biggest formations in one shot (and since armies usually have a mix of units, this lets the player prioritise what to spend their valuable firepower on—i.e. don't shoot the big guns at Sentinels unless it'll win the game—as a meaningful tactical choice).
If Imperators (say) are priced with killing 4-man Sentinel formations in mind, they'll be grossly underpriced against most opponents; 10-tank Leman Russ squadrons will probably result in them being overpriced in most battles. Their output will swing widely and only their resilience will really be a stable basis for pricing. Other formations suffer this problem too but it's much worse when you have a giant gun-platform.
Split-fire does make a formation more dangerous, no doubt about that! But for those few units at the top end of the firepower range, split-fire is one method to make sure an expensive unit is actually worth its price.