To put it a different way, vibranium really only does one specific thing (well, Wakandan vibranium). Cap's shield does that thing, but is a superalloy of vibranium+other crap. Which at this point includes the material Thor's hammer is made out of. I'm pretty okay with vibranium+something that even true adamantium is apparently a lesser version of* holding up to what it has (also now including uru)
*adamantium is the result of the guy who made Cap's shield by functional accident trying to reproduce it and never succeeding. Which is to say, durable as adamantium is, it is amusingly the equivalent of the made in Taiwan version of Captain America's shield.