I literally quoted you
I'm aware he's not a plus defender yet. The irony of you telling me to actually watch him play is lost on you. I have been for years, while plenty on this forum discredited his game because he's European and not a freak athlete. As has been pointed out, Curry, Harden, Nash and plenty more are/were all putrid defensively. I actually think Doncic projects as a better defender than all three given his size and the fact that he's willing to put in effort on that end. We've already seen him make impressive defensive plays against some of the league's best, as posted above (in your words, "go watch him"). He's never going to be a lockdown defender but he's a kid and will improve as his body matures and he learns how to play on that end. Many of the league's best players are just as bad defensively.
Continue burying your head in the sand, though. If you want to solely use last night's game to harp on your point, I'll say that the fact that he dominated down the stretch and led his team to a victory outweighs his defensive struggles. The whole point is to win the game.