The husbandry needs of just about any snake require a little homework and research. Reptiles in general are not exactly "beginner" pets in that regard.
Colubrids also need proper temperatures, security and species specific care. Some colubrid species are even more mellow than balls.
I could make the case that a gopher snake is every bit as affordable, is easy to handle, and is more forgiving of husbandry lapses compared to a ball. Yes, they require a bit more diligence in the way of cleaning, but I've been catching wild ones for years and find most to be quite docile.
Are ball pythons the most forgiving snake of husbandry errors? No. There are better choices out there, even in the python family.
Spotted pythons require almost the same living conditions, stay small, poop in small compact logs and tend to be docile and tolerate a lot of handling. The also are less prone to miss meals and are a bit hardier.
To get back to the OP's question:
Are ball pythons a beginner snake? Yes.
Are they the easiest beginner snake to care for? I don't think so.