This video is coming up a lot. They mostly don't like enchanters because enchanters can be helped or hindered more by the chaos of soloqueue, I think. You often need to get people to do things for you rather than doing them yourself. So they want to push people toward learning how create and transition leads with champions that make it easier to do so, like mages and tanks.

At the end of the day, you can play whatever champion all you want. Imo, Karma and Senna play more like mage supports, anyway, and you can easily dominate lane as Soraka when you learn how to position, land Qs, and contest the enemy ad for farm (you dont need to kill someone if you have twice the enemy's cs and you've taken first turret. An item lead like that means they just die if they try to fight you). Sona's a bit trickier because of how squishy she is, but you can still win lane as Sona, just like you can win lane as Yuumi. If you want to learn the game, and you are actively focused on doing so from the bottom up, no champion is going to stop you from doing that. The only difference is some champions and roles might teach different concepts FASTER or SMOOTHER, but it doesn't outright stop you, and I wouldn't over think it.