> In Excel, I change one or two cells and see everything update immediately
This is the problem - it's all too easy to change cells, misclick, and generally make mistakes. When you do things from a programming language, you need to be explicit about operations, and explicit about what changes you're making.
Spreadsheets should be for entering data only, R is for processing data.
All the examples of enter data, create a chart, oh let's change/update some data, oh let's add something to the file, etc..., are why you end up with incredibly convulated spreadsheets that inevitably are filled with errors.
Enter your data with whatever tool you want (spreadsheet works for this), then process it (R works for this), then shove it in a database. Nice and easy, not error prone, and every tool can have easy access since databases are ubiquitous.