There are also entry level M18 tools from Milwaukee, so you can’t go solely by voltage.
A Quick Look at the current Home Depot flyer shows deals on M18 brushless tools, but they aren’t the Fuel version, but rather simply brushless. These would be considered more homeowner level M18 tools, built and spec’d to a price point, rather than Premium Fuel tools.
Dewalt tools in the flyer follow the same pattern. The 20v tools being promoted, while brushless (I believe), aren’t the Premium XR versions .
Same with batteries. Both brands offer a couple of grades of batteries at different price points.
I mostly buy the Compact Atomic and XR series Dewalt, and M18 Fuel Milwaukee when adding tools, but also buy other brands, knowing they likely may not be equivalent, although they, so far, have done the job I bought them for. I haven’t yet been disappointed with any of my cordless tool purchases, regardless of brand. I currently have eight active battery platforms, and, from memory, have phased out four more over the last forty years.