There's something called "Brook's Law" that basically observes that a software project which onboards more developers in order to catch up will fall further behind. I hope they're careful about how they allocate new developers or they'll end up doing a year of onboarding, rewriting core code, and have no meaningful updates for 6-12 months. I know they have the resources to spare, and that scenario worked out okay for Valheim, but I hope the game doesn't lose momentum because they overhire or don't allocate enough senior devs to continue feature development while they catch the new devs up to speed.

Edit to add: I don't think it actually matters in this instance if they don't have a large player base by the time the game is feature complete. They don't have continuous revenue streams like a live service game, so hiring more devs is ultimately just about making sure they have enough talent to make good on their early access promises. The company could probably dissolve tomorrow and all the staff could live the rest of their lives in luxury never working again. It'd be a dick move, but they already sold an insane number of copies.