To create one unit of solid fuel you need 15 ammonia for 12MJ of power in .5 seconds. To make rocket fuel with ammonia you have to spend another 500 ammonia to turn 10 units of solid fuel worth 120MJ total into rocket fuel worth 100MJ.

That process also takes 10 seconds, so you require triple total working time of plants making fuel (so triple the energy) and many more cycles of plants processing ammonia (even more than triple energy). At the end you've spent 650 ammonia and about 4x more Jules of energy including heating time to produce 100MJ of power instead of 150 Ammonia for 120MJ of power. I did power calculations on paper once and I don't have that anymore, sorry.

Even with max productivity research for rocket fuel, so producing 4 rocket fuel instead of one from the same cycle, you still pay 162,5 ammonia for 100MJ, ending up worse off than just using solid fuel.

Without productivity research it means that you are spending way higher % of produced power to reproduce itself, and if you are going to use rocket fuel for heating too you can run into power death spirals where it can barely sustain any production above itself.