I don’t think he should “just deal with it” though: I think he should critically engage with negative comments, form his own opinions, and then trust those opinions over those of an Internet stranger.
Which maybe is functionally equivalent to “just deal with it”? Feels different to me.
Also I went to the Pathfinder2E subreddit, ran some basic searches meant to evoke comparisons to 5E, and grabbed the top result for each: “how do attacks work” ( https://www.reddit.com/r/Pathfinder2e/s/BBYlzCwVDl ), “advantage in PF2E” ( https://www.reddit.com/r/Pathfinder2e/s/Yna9TGzAOu ), “warlock equivalent” ( https://www.reddit.com/r/Pathfinder2e/s/umQ1Et6xhf ).
There are NO comments in ANY of those posts bashing 5e. On the contrary, there are dozens of comments that are all helpful, encouraging, and supportive.
So if you’re looking for a place that is generally positive and welcoming to new players, r/Pathfinder2E has been pretty good in my experience! It’s not perfect, of course. If you’re looking for a knowledge center that a) has people posting and talking and b) never ever ever portrays 5E negatively I don’t think that exists.
Anyways, hope your partner continues to enjoy ttrpgs regardless of the system!
Kids open their mouths when their heads are upside down - great way to quickly investigate what exactly they’re chewing on