21 laps is more than an hour, so the Toyota was still on a quicker pace, and that's against a Porsche that was really thrashing it over the last 4 hours or so to try and get to the lead. Different races and difference scenarios, but I don't think people can say the #8 was holding back, especially in Alonso's night quad-stint.
LMP2 decided after the race, G-Drive excluded for adjusting their fuel rig to gain about 6-8 seconds per pitstop (mounts up when there are 37 of them). They must be kicking themselves given they could have won on pace alone.