The problem with this argument is that software is not just a little bit slow, it is insanely slow. Like if you break down what Teams actually does, and count how many CPU cycles that should take with some quick napkin math, Teams is slower than that by at least a thousand times. Obviously this kind of first-principles thinking is idealistic, but the result should not be underperforming that by several orders of magnitude.
The real problem is just the general practice of how software is developed now. If we lived in a world where software development was sane, it would be possible to prioritize speed of development and cut some corners to ship faster, and get a result that is somewhat slower but not ten whole seconds to start up slow.