I think the X-Mid 2 is very similar to the Stratospire 2 in terms of weather capability, where both tents can be used in all 4 seasons but aren’t “4-season tents”.
I don’t think Tarptent claims the Stratospire is a 4-season tent. On the Stratospire page they list it as “3-4 season”. Their tent finder does say “use in all 4 seasons” but that is subtly different from “4 season tent”. I think they are saying you can use it in the winter, but not saying it is a “4-season tent” which generally means more than just winter use to also mean you can pitch it basically anywhere (e.g. exposed spots) during extreme storms (e.g. mountaineering use) and expect it to be fine. I don’t think Tarptent is suggesting that, and I don’t think any tent that uses 20D fabrics is up for that (the Strat is now 20D poly like the X-Mid) because 20D fabric is just too light for extreme storms regardless of the tent design.
My guess is that the beginner hikers in your group do not actually need a “4-season” tent but just need a 3+ season tent where you can use it in the winter as long as it’s not extreme snowfalls. Both the X-Mid and Strat work well for this, with each having some advantages but probably both are quite sufficient. As it pertains to winter/snow performance, the key advantage of the X-Mid is that the wall slopes are steeper so it sheds snow better, whereas the Strat has shallower roof panels that would be less inclined to shed snow – but really both are going to be fine if we’re just talking 2-6″ of snow. I suggest that more meaningful differences to the beginner hikers in your group would be the simpler pitch and lighter weight of the X-Mid. The X-Mid 2 is just as spacious as the Stratospire 2 but less expensive, already seam taped, simpler pitch, smaller footprint, and about 6oz lighter.