>>64492484 (OP)
Organic-looking curved lines, lots of cylinders that flow into each other and gentle transitions between surfaces.
The intakes, which are by necessity bulky and rough looking are placed underneath the body of the jet where they don't obstruct the esthetic flow.
And then there's the swan-like shape of it where the head is above the body giving it a natural appearance rather than the classic tube design where it's all in one line.
>>64492646
Making new jet engines is a difficult and time consuming process. They didn't want to retool Su-35 lines into Su-57 lines, make a bunch of them with interim engines and then rework those for the new engines afterwards when they have orders for Su35s to fulfil anyway.
As it is there's something like ~20 serially produced units with the interim engines. The next batch might have the new engines, probably.