Skimming that post shows a lot of people saying that first layer doesn’t affect top layer. What is your definition of z height? We may have a definition issue on our hands here. To me, it means the distance between the nozzle and the bed on the first layer.
I’d be with you on the underextrusion though if the very top layer didn’t look so good. I would bet OP doesn’t have enough layers on top of the infill leading to an artifact that resembles underextrusion.
Punchline in the title,
really?