I've never had a problem with the durability of the aluminum Weaver bases, on my .300 and 7mm mags, or my buddies bigger stuff.
Of the dozens had, I did get one set with the holes off center.
But then I've seen some pricey rings and bases by other manufacturers a little less than they should have been too.
Aluminum- one less thing to rust.
Slight flex (if it's there) might make for more solid anchoring of the base itself.
I only run cheap guns, like lowly Remingtons, it's not like I'm putting them on a Dakota or some classic Browning Safari bolt rig