There are two main issues my org has battled with:

1.People basically turn excel into their own mini databases which causes a support nightmare.

2. This is strongly related to 1) Data provenance is a nightmare because so many people were passing around excel spreadsheets it became very difficult to track down the source of the figures people were using. User A passed their spreadsheet to user B who modified it passed it to User C who further modified it, passed it to User d from there some figures ended up in front of a manager and now we have a problem...

It's not so much a problem with Power users those are the types of people using python (or R) it's the tier of users below that level that cause the damage with excel.