I've been hunting around for awhile and not found an answer so I figured I may as well ask. Most of the documentation say's Compassion (102) was the most powerful TARDIS with the 103, 104 and 105 models being deliberately built to be weaker than her. However by the 105's they were losing the war and that model had hundreds of eyes of harmony, the power to obliterate a star system and blockade entire chunks of time as well as being built specifically for war. So I'm wondering why was compassion more powerful than them, what could she do they couldn't?
I don't think it's about physical power. Compassion had free-will. The later TARDISes were deliberately kept in harness by the Time Lords so that they could control them.
I don't think it was that they were taught to serve yes but what I've seen especially in the TARDIS technical index indicates it was something far more physical.
"While the 103-form would have most of the abilities and features of compassion, some of his capabilities were deliberately capped, making him less powerful than his form-102 mother. Most notably. Antipathy required a symbiotic nuclei to traverse the vortex. Antipathy had been horrified to be born and horrified to be altered by the dwarf-star-alloy tools that blunted and capped his instincts and abilities"
Then he got sent on a suicide mission, ate his operator and defected. Which tells me they can only traverse the vortex with a pilot and even though they learnt to work with time Lords push them too far and they'll eat you. Still its the other abilities and instincts that interest me what exactly did they cap on him? Plot device does seem a good option for compassion and an unaltertered 103 though. It also works when you consider a 105 had hundreds of eyes of harmony when compassion and the 103s didn't so far as I know which would mean it's not just a matter of raw power.
The production 103 also mentions having abilities blunted while the 104 and 105 entry mentions rumours of having recidivist genes reactivated from compassion to make them more powerful.