Why is Sylas’ R so inconsistent.

Sylas R can stun if used on Kennen however he doesn't apply Velkoz’s passive if he steals that ult. You can argue that Kennen’s ult is useless without the stun but I’d argue that Velkoz’s ult is useless if it didn’t proc his passive. Similarly, hijacked R doesn’t proc brand’s passive, which is the whole point of the ult.

And don’t get me started on ult abilities that empower basic abilities. If Sylas steals Riven’s ult he gets bonus range on his Q and W. But for some reason stealing Illaoi or Nasus’ ults don’t give Sylas any reduced cooldowns on his W or Q respectively. However stealing Vayne’s ult even gives him invisibility on Q cast.

Can Sylas’ ult be more consistent please? It feels like the most consistent part of Sylas’ ult is revealing whether an ult that empowers abilities is coded to work with an ability slot number or a specific ability name.