Super Moto X does not come in 28" sizes according to Schwalbe web site.
If it were me, I'd do a Marathon Plus Tour in 28x2.00. Its flatless, has a 128kg weight limit and can be inflated down to 35 psi, although for a 225 lb rider thats not going to be such a great idea.
FLAT-LESS – WITH A PURPOSEFUL TREKKING TREAD.Asphalt or off-road? Everyday use or bicycle expeditions? This versatile tire always does the job. Its robust construction handles almost any mistreatment. Protected by SmartGuard, the most effective puncture…
www.schwalbetires.com
No matter what I would go a bigger tire. I know a 1.75 can be made to work, but I would prefer to spend a few bucks to have something working well under its limits rather than up close to them. Plus, the MP Tour is known as a lasts-forever tire. I've seen claims of 10,000 miles. I have two cargo bikes using them as a back tire, one approaching two years with minimal wear, although its the older tread pattern and not the new/improved one. I had the same decision to make on my first Bullitt as the frame specs say 1.75" tires, but I could fit 2.0" without rubbing, and have never regretted the change.
Schwalbe says sold out but Amazon still has some.
Gazelle does not report tire sizes so maybe they did. It would not be a surprise if they just moved to the 2.0" tire. 1.5mm per side extra is very close and doesn't require any component changes from the looks of it. Hard to see a downside to going to 2.0" so long as fitment is ok.