Continental GP4000 700C x 28 (actual 32 mm): 695 mm diameter
Panaracer GravelKing SK 650B x 43: 677 mm diameter
WTB Venture 47 650B x 47: 681 mm diameter
There is still a 14 mm diameter difference (7 mm radial difference) between the road wheelset and the gravel wheelset (with Venture 47 tires), which is a noticeable amount. I would say that instead of the gravel tires being undersized, it is the GP4000 tires being oversized, as the actual width is 32 mm instead of the rated 28 mm.
As a result, the BB to ground clearance is also affected by the different tire diameters.
BB to ground distance for GP4000 700C x 28 (actual 32 mm): 268 mm
BB to ground distance for GravelKing SK (650B x 43): 259 mm
BB to ground distance for Venture 47 (650B x 47): 261 mm
7 mm less ground clearance for the Venture 47 gravel wheelset, compared to the GP4000 road wheelset.