It’s not necessarily an either/or, it’s both seat and pegs and depends on what stage of the corner I’d say. Weighting the outside peg to setup body position early for the turn (pushing off the outside peg to move my butt and create a good lock on the bike between ball of foot/toe to knee locked into tank) allows me to absorb braking forces with the lower body. Mid corner there is some weight on the seat from the thigh and one buttock (I’m not lifting my midsection off the bike with the pegs), but majority of weight and force is being supported by the outside peg to knee locked on tank connection. Once the corner ends (i.e. I can go WOT), I’ll support the majority of my weight and acceleration forces with my butt on the seat and back of seat, but I still have my legs/feet supported by the pegs (I’m never 100% weight on the seat either).
I’ll stay on the right of the bike if I’ve got another right hander quickly ahead. If at corner exit, I’ve got a long straight ahead, I’ll go to “home position” as you call it, (most aerodynamic). If I’ve got a quick series of alternating turns, there’s no time to stay in home position, it’s knee to knee and side to side time.