I'm not sure how many MVPs are awarded to first baseman anymore (the weird 2020 season aside) but if his defense is good there and the bat is elite...I'm fine with it. If he can be a 5+ WAR player at 1B, that's pretty good. I wouldn't worry about his defense at first base, if he's truly elite at catcher at blocking balls in the dirt, I'm sure he won't have an issue scooping throws. He's a plenty big enough target, should have a wide radius to catch throws. I'm not sure about what his range would be but I'm assuming he'd be quick enough.