Is that ok? Marksman are different from every other role because they are so needed to fill a specific niche in every single team comp, specifically pushing towers. Is it okay that they all play relatively similar with minor flavor? Or is your goal to push ADCs into stronger niches like Kalista? 2/2

My opinions is that Marksmen are too similar (except for some of the examples you made, like Kog). I know the strong ADC players on the team disagree with that sentiment, because for them, there is a world of difference in how you play say Lucian vs Graves.
We think champions feel different when the rest of your team has to slightly change their strategy to really support and leverage your choice, and the enemy team has to do the same. "Protect the Kog" is a pretty clear example. I agree that since they many Marksmen are so reliant on autoattacks that it makes them feel more similar to each other than say mages are. It's something we want to try and improve for sure.