Yeah I think this is because the way war is portrayed in the past flash back in T1/T2 its really serious as is the nuclear bomb drop scene in Sarah's dreams and the there wasn't any macho bullshit like look at us we are so great which really hurts the films that follow because you don't get this true sense of dread that humans are under the thumb. Like the biggest joke in genisys is Kyle Reese having a six pack and being buff (Who ever thought this was a good idea even for fan service needs educating on the universe's lore) when in the oringal its clear everyone was starving and there raids sometimes failed really miserably and those who leap back in time suffer from Ptsd.
That to me is what really hurt the last three films there just not grounded in the sense of reality, you don't feel the stakes you don't care for the suffering because its such a thin layered view of war and wars impacts, where as the T1 feels like it has WW1/WW2 vibes while T2 shows a nuclear drop for what it really is a terrible killer that kills in seconds and is truly terrifying.