Personally (and as Norbie has indicated) I think the people thinking that the sprinter strut is weak is just a load of rubbish.
I have much larger discs and calipers on my modified sprinter struts and no issues have been encountered with the stub axle or the strength of the strut.
If I was at all worried I would get the strut gussetted, which I would do with any strut if it came down to it. But this is over kill on a road car, common for rally cars though.