That still doesn't answer the question of whether it is an upgrade/same level as defined by Hertz
looking at midsize SUV for a dummy booking, it seems that Jetta allows for 5 adults , 2 Large Suitcases and 1 Small Suitcase whilst the SUV allows for 5 adults , 2 Large Suitcases and 2 Small Suitcases and is also more expensive
There doesn't seem to be anything stating it as an upgrade, but the cost and capaicty doesn't suggest to me a downgrade
In the end, the OP can complain to customer relations if he wishes to and see what it says