Well, KTJ-3200 has 1.20 kg SFC. Compared to that KTJ-1750 delivering much less thrust yet has almost same SFC.
And you are comparing an engine from 1970s with an engine from 2020s. I don't think that would be relevant.
Nope. It is more efficient and tolerate higher power input without increasing the cooling requirements. Or the same power input with less cooling requirement.