McLaren have a really strong car now and could challenge for a good share of the spoils this year. Piastri is good enough, fast enough and mature enough to be fighting at the front with said car, alongside Lando (who is equally strong). Lando taking his sweet time to switch back was IMO two fold: 1) See if the Team back down, which is to say, are the team more behind me than Piastri and 2) A message for Piastri to say you won, because I let you.
That the team upheld their team orders is a great sign of integrity and actually, both drivers can now move on a drive with that reassurance behind them.
Lando, will, I suspect be feeling threatened in the team by Piastri's ability, and rightly so. The competitiveness in him at wanting to win himself and coming out on top within the team matters - of course it does, he's an F1 driver! I have to say like MV, Lando can quite quickly get a touch immature (can't they all) - but nonetheless, he needs to work on that - throwing his P2 hat on the ground for example and being a bit rude to LH as examples; both not necessary. Piastri stands out from this as quite the exception - he's so level headed. He's still feeling the pressure though, that little trip through the gravel showed that but I think we'll not see much of that sort of mistake from him again.