Space marines? Not really. Bulky armour? Yes. It is meant to help take shots from alien plasma weapons after all. Big guns? Yes. Again, the calibre of weaponry would have been chosen to meet the threat. Have a look at a PPK compared to a Desert Eagle. Both handguns, but very different in terms of scale, use, and "space marineyness".
I can see some of your point. The space marine idea has entered gamer's consciousness quite some time ago, so it's an easy idea for people to grasp onto. Aliens+armour+big guns=space marine to many people. It's kind of a pity that people's own narrow view of sci-fi allows them to identify with this concept so easily (and sometimes only this concept). Aren't there 10 marines to a normal tactical squad? Aren't they all hard as nails from the get-go, even without their armour? Aren't they quasi-religious nutters with all kinds of iconography and "lore" that goes along with the space marine concept?
I see the point about smaller squads giving a reduced sense of scale to XCom. For some reason my brain thinks of 6 troops and puts in the "must be special forces" tag joined to it, where-as 14 troop squads could be anything. It probably does make each troop a bit killier too (or will spread the kills more evenly around those 6 troops, the original often had a huge disparity of kills amongst your team, especially with laser pistol scouts dying all the time). I'm pretty sure that without good tactics your guys will be plenty squishy as well (even in power armour), something that marines aren't. Special forces, yeah, I could see that. Using the best tech earth has to offer (or can research).
But space marines? Because they've downed the squad size and upped the kill ratio a bit? Sounds pretty simplistically thought out as an argument.