When I first got my back up pump + cartridge filter on trolley to clean my pool fast, I had the chance to experiment water flow loss with and without check valve. I think the one I was supplied is a lousy one. If it is a good unit, I don't think the loss will be this high.
I recall some valves are not full flow or the opening is not a 100% of the diameter of the pipe, I think this is the same I have for a check valve.
I think it will make a lot of sense to use a very good check valve even though it cost more, since loosing pump flow is like paying $$ for bigger pump but getting smaller pump equivalent flow.
Maybe use a bigger check valve and use a reducer, and we may get better flow.
This is a 1.5HP Pentair pump water flow without check valve installed on suction.