The easiest solution is for frigates to stop giving the Titan exp once it reaches level 2 or 3. That means you can beat up the Pirate Base for a free level then maybe one more and then you need to start taking on real fleets.

I can agree to that the Titan needs to lose levels when they die, and I assume that there is a change coming to the titan leveling.

I think that when titans die and are rebuilt, they start at Level 1, however you can spend Credits/Metal/Crystal/Whatever on it to retrain it back up to where it was. (Similar to how you can buy levels for caps)
Naturally the price increases for every level, with 2-5 being relatively cheap, and the levels after that should be a considerable investment.
This however punishes the player even more time-wise and economically for letting their Titan die.

titan need to lose lvl but not all the way back to 1 if its a high lvl titan

so if a lvl

1-3 titan is destroyed its reset to lvl 1

4-6 titan is destroyed its reset to lvl 3 with a cost increase

7-9 titan is destroyed its reset to lvl 5 with another cost increase

10 lvl titan is destroyed its reset to lvl 6 or 7 and another cost increase