Table view grouping issues:
1. formula calculation precedence options should mirror aggregation (formula result per field, rather than view-wide precedence setting)
2. wysiwyg, i.e. you have to show fields for them to work in formulas precedence setting (because otherwise you can't configure the mean/sum function for hidden fields)
3. you can currently only group by category fields
4. you can't show summaries in blank collapsed grouping columns
5. memory-inefficient

Ideas: improve the options so it is identical to aggregation, except the aggregation fields are in a chosen order, and you can expand/collapse them, and sort the resulting data.

Or, consider merging aggregation with grouping, by making aggregation have the collapse/expand capabilities currently only available with grouping.