How many Jedi were there at the end of ROTJ? I really don't believe numbers have much to do with why they chose 300 years after TSL.
Personally, I would have been much more for the Jedi facing nearly impossible odds than with a leveled playing field. When it is naturally expected that the Jedi would win 300 years down the road, then it seems a bit ironic that they would be beaten out by the True Sith when they were at full strength.
This shows that even after almost becoming extinct, the Jedi still didn't learn anything from the Mandalorian and Sith Wars. That completely demeans everything in the KOTOR story if they recover from those wars only to be crippled again by the same enemy.