Dreamweaver does not actually have an autoprefixer, (unless you want to use its sass/less function). The code you are seeing for gradients is all there is, and that is set in your Dw preferences.
I have been asking for the function for 10 years now, but those who make the decisions on such things do not think it is something Dw users want, or require.
Are any inbuilt prefixers up to date these days as in the example shown, transition you wouldnt require any prefixes, unless you are supporting less than modern browsers. Im guessing a lot of inbuilt prefixers may be bloating out the code when its unnessary, unless they are updated frequently.
Only the autoprefixers that one can set the number of browser versions back, are 'up to date', and that is because all such autoprefixers check with 'can I use' to decide what prefixes are required.
These days it is not so much desktop browsers that autoprefixers are required for, but mobile devices, game consuls and smart tv's that require them. I have even come across new android smartphones and tablet devices that are starting to use older versions of the OS, probably because of cost, (android is no longer 'free to use'). So prefixing is probably going to be a requirement for several years to come, (at least).