"but anything that reduces horiz scan power also reduces EHT, and vertical scan too if that runs on a LOPT derived rail"

True, but it does not stay linear. The vertical in this vintage of sets is like an amp that simply compares the current output with a ramp waveform. Frequently, the ramp waveform stays the same amplitude because it is further regulated, which then overdrives the vertical because the B+ to it is low. They cut it pretty close to keep the dissipation down. A smaller heat sink is cheaper. And most of these ICs are in a family, like LA 7830, 7831, 7832, 7833 with the highest number having the best max ratings. I would always replace them with the highest rated one in the family since they are otherwise identical and with a quantity price break the better part may actually cost less, but on a manufacturing level it pays to custom choose only as much as you need because on a million units a small saving adds up. Possibly to a bonus for someone.