Gunblade has no cast time?

So I was spamming Katarina combos in practice tool trying to find the quickest and best combos when all of a sudden I realised that gunblade had no cast time.

Two issues came to mind when I saw this:

1. Gunblade is pretty broken as an item why doesnt the active have a cast time.
2. If it doesnt have a cast time why does it cancel Katarina Ult if it doesnt have a cast time?

This makes no sense to me and people from the Katarina mains discord say its intended. I personally do not see why this should be the case as this would make combing so much easier for the champion and probably others, and if this is intended than why doesnt it just have a cast time right away? At least with a cast time you could use to to animation cancel a bit.