The issue here is you’re using an oil designed for racing in very low load, low rpm application and expecting it to burn cleanly. Dominators job is to keep a race engine that runs on the very edge of its capability lasting (for a relatively short period) under extreme conditions before being disassembled, cleaned and rebuilt. Some have success in saws because they tend to be under much higher loads for longer periods, but this isn’t what is commonly seen with weed eaters, especially 4 mixes at that.
I’d suggest you use an oil designed for garden power tools.
Edit: This is how dominator is designed to be used - listen to the engine, it will hopefully drill it home that it’s not for OP3… these engines will run like this for about 10-20 hours with how this guy is riding before teardown and rebuilds, that can be stretched to 60 or so if it’s not ridden so hard. OP3 with the right oil will last thousands