Re: So let me see if I understand...
If you test engine gimballing over its full range while in flight you will also test the vehicle's performance in pointy-end-down configuration quickly followed by an ambitious lithobraking manoeuvre. With enough duct tape the booster can be strapped to the test stand and remain flamy-end-down whatever you do with the thrust vector controls.
On the space shuttle the hydraulics had to work days after the hydrogen tank had been emptied and dropped into the ocean so they were powered by hydrazine. Hydrazine is sufficiently unpleasant to work with that hot high pressure hydrogen is actually easier - especially as you have 4x RS-25 engines each producing more than you would ever need to power the hydraulics.
Someone sensible proposed testing this new power system by gimballing the engines over their full range about one minute into the test (when the rocket would start to tip over onto its side when in flight). I assume the relevant politician leaped out of his seat jumped up and down with excitement shouting "Yes! Yes!!", calmed down and ask what was the largest amount of money taxpayers could contribute for this without looking completely silly.
On the plus side the test covered a range of motion that is extremely unlikely on a real flight. The power for the hydraulics is provided by multiple redundant systems and failure of any one would not cause loss of mission, let alone loss of crew. On the minus side this was not a SpaceX experiment with manufacturing test article 9 performed with test article 10 ready, waiting and using much needed space in the high bay. This was a verification of years of simulation and modelling that was supposed to prove the design before any construction even started. A sensor reading out of range shows there is an important detail missing from the model that makes the simulation invalid.
There are two obvious ways to proceed: identify the missing feature of the model, re-do all the simulations, correct the design and manufacture a new booster. Or you could just widen the acceptable ranges on the sensor data.
Normally I would expect congress to wet themselves and vote "YES!" to any opportunity to increase the costs and extend the project for another two years. This time there is a huge deficit, a trashed economy, a pandemic and Republican senators will riot over any spending where the Democrats might possibly be able to take some credit. On top of that SLS's days are numbered by the progress of Starship. Extra delay just reduces progress before cancellation rather than actually increasing the number of welfare cheques to Boeing.