I think that played a significant role too.Similar to what you're saying I thought The First Duty was Wesley's best episode. He wasn't nearly as one-dimensional in that one.
I think people would relate to Wesley a lot more if he hadn't had such a completely bland and terrible chemistry with Beverly. Compare their interaction to Sisko & Son.
Come to think of it Gates MacFadden's acting skills are probably worse than Wheaton's.
I believe that conceptually Wesley was a fine character, and a decent idea. He could have been likeable, even while retaining some of the characteristics that seem to make him unlikeable right now. He could have been a great character who shows that people can outgrow their age, and accomplish more than society gives them credit for, in a believable way. He could given a children's vigour and excitement to the journey, and truly humorous take on his own immaturity, a well-thought different perspective that his young age could have created. He could have painted children geniuses in good light, as relatable people, and not as someone who'd you want to smash with a baseball bat (that's how I felt about him when 12, I'd reckon the adult audience was a little bit less extreme).
I just don't think you can approach such character so casually. He should have been written better, and with more thought put into him. I think something was wrong at the heart of their take on him. Consider how even an experienced adult such as Picard was immediately looked upon with prejudice from everyone when he happened to be in a child's body. You'd assume that both Starfleet personnel and the writers would know better than that, but turns out they didn't. If you can't fit adult Picard on a starship, how can you fit an actual teenager?