There is a very practical reason for not having Sonarr rename WEBRip to WEBDL. It prevents programs like Autosub from downloading the correct subtitle, or in some cases any subtitle at all.
In general I don’t download WEBRips to avoid this problem (using an Restriction). But when there is no choice, I download the episodes manually. I then have to go into the TV series folder and manually rename the files to get the correct subtitles.
Is it really that much trouble to include WEBRip as a separate source (which it is), instead of renaming it incorrectly to WEBDL?