SPG had a "low threshold for top tier" and was "more egalitarian" only if you discount 1) far fewer properties globally (making one have to be more loyal to the chain), and 2) all the ways Marriott had to gamify nights, and 3) ignore the list properties received showing suggested upgrade order (which favored higher-night Plats/Ambassadors). Other than all that, sure.
Nothing stopping any hotel from seeing which Ambassador guests are coming in over the next 7 day period, rolling, and pre-assigning upgrades. No need to blame SNAs.