I think that's a reasonable guess. If a full boost 87 octane costs 8.5-13hp, it might be even less in first in second gears. Alternatively, you simply may not notice it, there's not a huge difference.
Can you point to evidence of that (a greater quantity of additives specifically for cleaning valves)? Additionally, do we know if "more additives" is comprehensively better?
I agree with your point about power, cars can be fun for different attributes. My last car had 455hp and I don't miss it.