With regard to Titan balancing, I'd treat them a bit more like WW2 era tanks since they seem to fill a similar role (hard to kill, tons of damage, expensive to produce.) One game that already takes this concept and does a really good job of it is Hearts of Iron. HoI4 has base tank models with optional sidegrades that increase specialization at the expense of other areas like armor or sacrificing certain damage types. As tech improves, you start by upgrading the base model and then you can research into the sidegrades for the new base and upgrade those as well.
For Aurora, I'd recommend having a base Titan model (upgradeable over time) that has all-around damage/defense capabilities. It's this base model that determines the overall power level of the titan. You could then have a sidegrade that takes that base model and re-imagines it to focus around anti-Titan capabilities at the expense of everything else (taking off some small arms in favor of more cannons, for instance.) You could also have one for anti-infantry (or whatever you're calling your regular ground forces.) You could even have one with some basic ground-to-space capacities, like meson cannons that can shoot out of the atmosphere and hit things in very low orbit, or act as point defense, or possibly even some light missile capabilities. Each of these sidegrades could then be upgraded once the base model is also upgraded.
It's an Aurora analogue to the HoI idea of regular tanks, anti-infantry tanks, anti-tank tanks, and anti-air tanks. The player has to decide how much of each to build and include in their military in order to counter whatever their recon suggests they might be up against, which makes for pretty interesting gameplay provided the recon and production aspects are engaging enough.
Another alternative is to just have research branches that allow us to upgrade the various aspects of our titans as we see fit. This runs the risk of not having any sidegrades, as you'd just always produce the best available suite of upgrades instead of having specialized Titans.