Skarner Actually Feels WEAKER
I was optimistic about these changes but my perspective changed completely after playing with them. His spire vision was a huge part of his power. Being potentially tracked by the enemy is negligible compared to having vision of them and seeing when they take your spires. He lost so much more power than he gained. It's actually massive. This is definitely not a buff overall and it feels awkward not to be able to quickly see which spires you even have under control on the minimap or their ranges. Not only is he weaker but he is also less satisfying and the spires feel more gimmicky rather than core to his identity.
BTW: While it's true that enemies don't see you captures spire either, this wasn't really an issue. If I wanted to gank, I wasn't going to capture the spire on the side I'm going for the gank anyway. I'd gank first and then do that. In fact, you could even play mind games with it.