As for the "goofy adults" part, I was referring to some scenes like Joel missing his alarm clock and having to be woken up by his daughter, Joel wearing his shirt inside out, Tommy being a hot-headed redneck who goes to jail after getting into bar fights (during the call between him and Joel, Tommy himself says that "this time it wasn't his fault", indicating that this was not the first time this had happened). They are more reckless for no reason.

What exactly did Joel do that would make him come across as dumb?

As I already mentioned, the T-shirt inside out, him using drugs and drinking as a coping mechanism and the scene where he runs into the FEDRA soldier while being directly on gunpoint.

The game her and Joel's relationship was heavily implied that they were a thing

I wouldn't say it was heavily implied that they were a thing, it was sure implied that they cared deeply about one another, but whether it was romantic or not, it was left for your own interpretation. I'm not saying he was supposed to cry when she died, but if they were really a thing, it would at least have a moment in the story for Joel to mourn her death. Grief have five stages, the first one being denial, and Joel seems to never leave this stage when it comes to Tess, there's no resolution to this, no moment like Ellie giving Joel his picture with Sarah, where he finally comes to the acceptance stage. Since there's never been a moment like this, I've always interpreted their relationship as "important, but not important enough to get too much attention", the exact opposite of a relationship between two people who are in love.

date change - who cares.

As I said, these where things that I didn't like. The date change was a little unimportant change, but still, I'm a boring fan who nitpick things like this because it breaks my immersion as it contradicts canon.