It’s a bit tricky with the crankset change you're thinking about. MTB front derailleurs are usually limited to a 10T difference, but it sounds like your setup is already pushing the boundaries with 12T and working fine. The road and GRX derailleurs can handle a 16T difference, but yeah, the pull ratios are often different and may not jive with your XT shifters.

One option to consider is a "wide-range" MTB FD that’s specifically designed for larger gear differences, like the Shimano Zee or Saint series, but you might still run into the pull ratio issue with XT shifters. You could also try adjusting your current setup or going with a combo of road/MTB components that are compatible. Just be ready for a little trial and error.