[mjevans]

The BOM can vary quite a lot between 'revisions', using your product as an example...

https://openwrt.org/toh/tp-link/archer-c7-1750 (Scroll down to the Info Links table and the Wikidevi Info column)

v1 to v2 upgrades the Flash (8MB to 16MB) and uses a slightly different AN+AC wifi chip. v2 and v3 seem pretty similar at a glance. v4 is rated at 12v 2a rather than 2.5a; using a completely different BGN(2.6ghz) chip and also different ethernet chip/switch. v5 is lower power still at 1.5a, but it's less obvious where that change happened due to lack of pictures. A guess based on the simpler antenna list is that it uses less antenna.