I think you are looking at this the wrong way... As for the website crashing on reservation day, they got millions of hits to their site, and frankly did not expect that, and were not prepared (no big deal) Tesla has also had their website crash during the model 3, Y, and Cybertruck unveiling. As for the Mach E comparison, Mach E did not have near the interest the HummerEV did, just look at click counts on online reviews (the only way to get high clicks on a Mach E video is do a Tesla Y comparison in the title or thumbnail) Mach E has also had its share of controversies and problems with last minute delays, and dealer gouging. Fords website did struggle on the Lightning unveil, which got far more interest than the Mach E, and on the Bronco, they crashed totally. Personally I did not like Ford's reservation system and had trouble logging in for the Lightning. I got errors and disconnected a few times and gave up.
As for Communication, GM has been about as transparent and clear as any OEM I have seen on the Hummer Ev status. GM guided when they started taking Hummer Ev reservations that first deliveries would be in the fall of 2021, AFAIK that has not changed. GM has publicly reiterated this guidance in press release after press release, and has shown videos of their test program, and factory setup almost weekly.
As for GM's online accounts, you should write to them with suggestions, this is all new territory for GM and they are winging it a bit when it comes to this style of reservations system. Post on the GM twitter account, and they will reach out to you via DM for suggestions. I think GM can get better in this area, and the integration between the dealer, and Corporate could use improvement for sure. The way GM is doing it now is taking the reservations, then transferring it to the dealership along with our deposit.