So, assuming you're still on Office 2010, you're missing (off the top of my head, but I believe these were all Excel 2013 or later):

• Initial support for super-large spreadsheets, with accompanying perf improvements (this was maybe 2013?), and then lots more perf improvements in 2016 and 2019 as people started using those really big sheets;
• Flash Fill support, which is kind of like an AI (not in the ChatGPT-sense)-powered fill down (so e.g., nowadays, if I enter "Sept 6th" and then "October 4th", then it'll offer a completion of November 1, since that's the first Wednesday of the month);
• Heavily improved Pivot Tables, including Slicers, Power Pivot, and Pivot Drill Down, which make exploring data a lot easier;
• Forecasting tools; and
• Much better Tables, making it a lot easier to write formulae entirely with named references rather than cell IDs There's more, but that's what I could remember off the top of my head/could quickly verify so I was sure I wasn't misspeaking. LibreOffice Calc unfortunately also lacks basically all of these features (and the lack of Tables in particular means that OpenOffice sheets still have a lot of A2:A300 garbage where Excel would instead just have e.g. SomeTable[Heading]. E.g., an actual formula from a sheet I currently maintain to track my team's sprints: =XLOOKUP([@Verified],SprintMeta[Start],SprintMeta[Sprint Name],"Unknown",-1). Python's easier to read here, but this is honestly doing a lot while being surprisingly readable (especially if you're familiar with XLOOKUP, which is basically how you do keyed array access in Excel)

You have totally legitimate gripes about Excel; I'm not denying that. But I do think that you might be pleasantly surprised on newer versions.

This feels like a really dated take to me. Leaving aside whether this was true in the past, in 2023, Excel is happy to open absolutely gargantuan files, and it's quite speedy once it's done so. You can even directly tie it to a database via ODBC if you want, and that works (albeit it obviously flattens the data out in the process, so goodbye foreign keys in any real sense). It also has tons of very easy-to-use data manipulation tools (pivot tables, tables in general, data extrapolation, graphs, etc.) that end up being wonderful complements to something like Python.

Could you write a Python program that would run faster than pure Excel and do the same thing? I mean, probably (although Excel's core execution engine is honestly pretty freaking fast). But could you write it as quickly? Maybe, maybe not. And certainly someone who knows Excel well would have an easier time adding a little Python to patch up any issues than rewriting the whole thing from scratch.

tl;dr I think you're not being accurate about contemporary Excel, and I separately suspect you're not really the target audience here