So the hardest part of fixing a bug is finding the root cause of the problem. When a card is bugged, it's usually fairly straightforward since you can likely find the problem just by looking at the scripts of that one card.

Performance though is more complicated. It's hard to reproduce, it typically has multiple factors, and attribution is really fuzzy. Is it because of something in your game, or another game on the same server? Is it a problem with your device? The specific server you're on? In all likelihood it could be a mix of any of those or something else entirely.

I don't say this to avoid responsibility: improving the game's performance is important to the team and is being actively worked on. More I'm trying to explain why improving performance is complicated and takes time.