One of the things that really winds me up about the ESRI platform is the lack of consistency across the system. The latest one I discovered concerns field names that you can't use in hosted tables in ArcGIS Online. I was creating a hosted table directly in ArcGIS Online to store details about other hosted feature layers, including their size and access restrictions. In ArcGIS Online, if you try and add a field using the name 'size' or 'access' you are presented with a message saying 'The field name cannot be the same as an SQL keyword':

This is fair enough, however if you create a table in ArcGIS Pro with fields called 'size' and 'access' you can publish it to ArcGIS Online without any issue.
I find this inconsistency really frustrating. If it's possible to publish a table with the field names of 'size' and 'access' in one part of the system, they should be permitted in all parts of the system. My idea is a simple one really: ensure that the system behaves consistently across all components. In this specific example, a change needs to be made to the Add Field function in ArcGIS Online to allow SQL keywords to be used as field names, as they're clearly permissible depending on how you create the table.
There are so many other areas of the system where there are inconsistencies (feel free to add specific examples to this idea), but this one really annoyed me and prompted me log it as an idea.