I found the same thing. The joint between the camera body and the grip is as strong as the camera body directly to the tripod. The problem seems to be the tripod mount of the grip itself. If the camera amd grip is mounted to the rrs L bracket I can easily flex the camera back and forth such that the only thing stopping the camera from flexing more is the camera strap loop hitting the indent in the rrs L bracket.
Wow. Flexible polymers on the base of the grip instead of Mg- alloy! I doubt any concern about Wifi signal transmission was behind that...
EOS 5DIII, EOS 5D | Rokinon 14mm f/2.8, TS-E 17mm f/4L, EF 24-70mm f/2.8L II USM, EF 35mm f/1.4L USM, EF 40mm f/2.8 STM, EF 100mm f/2.8 Macro USM, EF 135mm f/2L USM, EF 70-200 f/2.8L IS II USM, 1.4x III, 2x III | 600-EX-RT x3