Titan seems to mean (at least in Dresden universe terms) proto-god.
These gods are primal elemental forces of the universe. They existed, according to WOJ, before Reality was made...in some form. So did the Angels. Consider the almost personal interaction that the various angels and beings have with Ethniu.
The new gods are Mab and the like. Mortals with mantles.
Sibelis is onto something, I think. I think the distinction between Gods and Angels is more about where they draw their power from, but in terms of origins they are all about the same. Considering the fact that they a existed
before time (if you can really have such a thing), I would say that who is older isn't really relevant or even something that can be answered. Cause and effect didn't exist yet!
Just remember you've got to include an explanation for how that jacked them up enough that they have archangel tier minions.
My theory has always been that the "Walkers" and such beings are the equivalent of archangels and the Old Ones are TWG level. But the main difference is what they are. Destroyers versus a Creator. I suspect the Old Ones cannot create a universe or anything meaningful, and therefore are unable to truly combat TWG. They can only destroy things, but they never can solidify or capitalise on territory they reclaim via destruction. TWG by contrast is taking up all the real estate with Creation, and every win grants even more space and makes it harder for the Outsiders and Old Ones to get that space back.
But that's just a theory.