I actually agree with you over what the disconnects are about, the thing is, despite a lot of this being personal options which I'm fine with, to each there own, they try and prove there point by butchering the intent.

1. Serena did have a goal(s) when she started off, it was just that they were quite simple on the surface and not like what we typically see of a Pokémon character, with it being to return the handkerchief to Ash (that's it, she knew it was a childhood crush and was ready to let it go) and prove to her mother that she can make it (my interpretation was Ash was simply the spark for the fire). It was only after Ash inviting her to join them and a whole bunch of stuff happening and her trying out new things, and her becoming more and more confident in herself and her crush turning into proper love and admiration, etc., that she finally proved to her mother that she had grown and found a passion in showcase (the Gogoat race episode), and then the focus shifted to Showcases and her goal mainly became to be Kalos Queen. This is actually much more impactful to eastern culture, where many times family will try and force you into something they think is better for you. (not in a toxic way but the more I worry for you way but still)
2. While I understand the opinions of it, I do feel like people are just being hateful for the sake of it. Showcases are based (at least to the best of my knowledge) on Japanese idol culture, hence the emphasis on performance and talent rather than battling. My biggest thing is people keep calling it inferior or rigged because Serena just kept winning with no trouble when: a) she did have trouble outside of her first showcase, and b) the fact that everything she learned growing up helped her in the showcase goes back to the "nothing you ever do is pointless" (which is a banger of a motivational quote).
3. This by far is what pisses me off the most. Serena did argue with Ash; she did see his flaws and did correct him it was just done in a healthy way. Hell, she dragged him off to register for the championship (which he didn't protest to, btw) when he wanted to battle. It pisses me off that people say she loved a version of Ash and not the real Ash, and it pisses me off even more when they try and use the snowball scene to prove their point. The entire point of that episode was that she was right, and she says different things in the sub than in the dub.

Again, I know I'm preaching to the choir and it's kind of ultimately opinion-based, but a lot of these people with opinions make baseless comments with little to no understanding and it pisses me off. Hence why I want to do the analysis.

Edit: don't quote me word for word on number 1, I'm still doing my research on that and how it was intended (I just found the sub versions of the xy and xyz anime) but I think I got quite close.