Both units frames are constructed with the same stock steel with the same lifetime warranty. The X1i is a couple of inches shorter. The VX4 deck has a different grass flow design and requires more steel because of it's physical size. Both decks constructed of the same steel and have the same lifetime warranty. The Parker drive is similar to the ZT3100 in design and has a warranty of 2 year 1200 hour for the commercial user or a 5 year 500 hour for the residential user,not sure where you got the 750hrs. The integrated drive systems have come a long way in the past 5 years. Is it better than the separate pump and wheel motor? That's a question of old school vs new school. 5 years ago that was an easy question to answer, but with the advancements of the integrated systems with their light weight, compact design and durability in not too sure anymore. I'm always mindful of the cooling in a hydro drive system. This new Parker is wide open with plenty of ventilation. Heat is your enemy in the hydro world.
With a smaller physical deck, shorter frame, lighter weight drive system, smaller engine, these all add up to about 200lbs lighter footprint.
Hope this helps,