You are correct. App Lab doesn’t do multitasking well. You can’t time it accurately anyway. We must remember that App Lab is a Javascript interpreter running on top of a Javascript interpreter. It was never intended to run fast and criticism for speed is unfair. I suspect the database is actually a text file on the server and the whole file is transferred.
But my point is it is probably good enough for student sized projects. You and I have talked about slow connections in China before Does update/read/createRecord return an error where there's a timeout?. Perhaps you could ask for an offline version that stores the database locally.