Presumably most of the firms clients are themselves hosting email on Workspace or 365. And Google/MS might treat email originating from their own systems differ

Presumably most of the firms clients are themselves hosting email on Workspace or 365. And Google/MS might treat email originating from their own systems differently than inbound email originating elsewhere. Also I'd expect all the firms competitors to be using Workspace or 365, so if using them gives no apparent protection, presumably they should be suffering from this as well?