Why is bulky a problem for all-day? I wear 661 Rages, no problem wearing them all day (soloing the glentress seven lately, frinstance). Slimmer pads would have been no advantage.
Restriction, heat and comfort, sure, but that comes from fit and design not bulk, a good bulky pad can be better than a slimline one on all those points. The basic designs mean that often slimline pads are very enclosing, and relatively tight. My gform elbow pads are far, far warmer than my massive POC Bones- they cover more skin and they’re tighter.
IMO the only reason to wear slimline kneepads is that you want to wear trousers. Other than that, maybe your ideal pad might be a slimline one but not for that reason.