I couldn't find any dell or hp workstations that go over 64GB in RAM. The Mac Pro goes up to 1.5TB. Apples and oranges.
[1] https://www.dell.com/en-us/work/shop/workstations-isv-certif...
[2] https://store.hp.com/us/en/pdp/hp-z8-g4-workstation-customiz...