I think Asana tries to upscale. It is easy to make a solution for a single person or a single team, but when you try to create company-wide platform (as Asana tries), it is inevitably leads to complications like Workspaces/Organizations/Projects/Teams. Domain model becomes complex and it is still a monolith, so performance degrades. We have exactly the same problem in Targetprocess. So slowness is kinda explainable.

However, on my opinion products like Trello and Asana will have hard time trying to scale. Most likely we will see new products that will take this segment by storm, like Slack in work chats niche. All current solutions are not good for organizations.