I feel like old stuff always feels way slower than I remembered when I revisit it years later. I couldn't believe how slow of an iPhone I lived with when I booted my old one up recently.

Plus, most of modern Excel's apparent slowness comes from the animated text input and the animations between cells in the spreadsheet. I think that the text animations could be safely removed, but animations that give users a sense of relativity on the 2D plane when they make movements are very useful for UX.