yes this is the size in inches, or approximately the size, as there are plenty of razors labeled something and being up to 1/8 larger (and if you check the recent Thiers-Issard thread in this section you'll see that sometimes they're smaller than advertised too).
5/8 is not too small. It's the most abundant size, which should actually tell you something. Plus the more a razor stands out for whatever reason, the more chance it can become a topic to talk about, that has nothing to do whether it is any better for using.
Other than that, apart from larger width, larger razors have more weight, which has just as much if not bigger effect on shaving.
You should get something close to the standard 5/8 hollow grind.