Not saying that Umbrella is better for all, but as you say, where end client has made a blanket decision not to use PSC's (which I understand but don't support), a compliant employment Umbrella is an appropriate solution.
Best advice process to workers still applies; PSC .v. Umbrella.
For more details on why the compliant employment Umbrella model is here to stay;
Call it what you like, the compliant employment "Umbrella" company understands its role as a "PEO" and has been delivering this service for many years. Demand for Umbrella employment has indeed increased considerably since April. The King is dead, long live the King.