Thanks for playing the game! Unfortunately, the web build does have problems with loading the shaders, causing those lag spikes, though once they've been cached the lag should go away for that session. Though if you could play it with the Windows version, that would be better (way less lag, way better graphics).
I think dragging the cards from the bottom is the core mechanic of the game that gives the nice deck-building vibe, so I guess it just needs some getting used to. Also, I can see why it might be difficult, though I think it has to since it's a fast-paced bullet hell, and the difficulty is what gives the adrenaline.
Hope you give it another shot!