In order to hurt the larger coalitions and entities though, you would have to make it scale on a level that makes it untenable for smaller groups. We need a system that hurts larger entities but doesnt necessarily hurt smaller ones. Upkeep hurts it all across the board, evenly.
So I actually presented this a long long time ago. Having a non-capital ship with viable anti-capital weapons, even if its dedicated and only one-time-use would definately give smaller groups the ability to destroy larger enemies without the need to ship into capitals themselves.
The problem with your idea is that it doesnt fix the N+1 problem of capitals. The other side will still be able to afford dozens of titans while you are unable to afford a single one because of both costs and upkeep. They may not be able to afford 500 anymore, but even if they were only able to afford a mere 50 titans, thats still a lot, lot more than what you would be able to afford.
We dont need LESS of them. We need to be able to DESTROY them.
Edit: Sorry i should say we dont SIMPLY need LESS of them.