I will actually agree that, purely looking at the two projects from a construction volume standpoint in a vacuum, the SFMM coaster is probably more difficult—tons of footers, tons of terrain, lots of land stabilization work, California building regulations, lots of impediments around the site, etc.
That being said, the SFGAdv project is much larger in scope overall (remember: we're anticipating a fair amount of theming and a significant overhaul to the surrounding area), far, far more daring from a technological standpoint (meaning longer testing and commissioning times most likely), and, weather wise, working in SoCal is a dream compared to working in Jersey (SFGAdv's construction season is way shorter than SFMM's). Oh, and SFMM, being a year-round park, also has far more flexibility when it comes to ride debut windows. It could make sense for SFMM to open a new attraction late in the summer or even during the winter—SFGAdv really has a much narrower window during which they can stage an optimally successful attraction debut.
The future of many parks in the chain are uncertain at the moment and I'm not going to say that it's impossible that your pessimism could be proven correct eventually. That said, I don't see a reason to buy into it for now given the publicly available evidence.
Most everyone with a Six Flags park has their home park is at least vaguely spooked right now. SFGAdv is in an above average position though if you ask me.
