When you delve into badly-performing web apps, DOM is almost never the actual performance bottleneck. It’s other things they’re doing. And in the rare cases where DOM is the bottleneck, it’s always that they were abusing it.
As for this case, I have never encountered a web app with performance (throughput and latency) problems like this. Not anywhere near it.
Similarly I don't think canvas is the bottleneck here.
Oh, and abuse is the name of the game. Almost exclusively the only thing the browser deals with is abuse. Logical consequence when the users are the one paying for it.