I have had this issue for a while, and this week I decided I was going to find a solution. I work in a firm that is an all Mac environment and we are constantly snapping a pic on our iphone and then airdropping to my Mac desktop or ipad to send/upload to something.
I found a tutorial online using the Automator application that came out in the last OS update. (I kind of forgot about this feature, and was initially excited about it when they made the announcement.)
Here is a link to the tutorial.
I did not use to function to "copy finder item" as I did not want to keep a copy, but this is awesome. Now when I Airdrop a photo in the finder I have a widget shortcut that will convert this image in the finder and replace the HEIC version with a JPG. Hope this helps some of you, as it has been awesome for me!
Here is a screenshot of the end result for the shortcut:
There is a lot of really cool things you can do with the Automator tool so check it out!