I totally get where you're coming from, but in fairness to Moore it's not his fault there were so many candidates in this race. Hell, Baker, who withdrew, came in fourth place. Actually, I'm wondering if Baker dropping out is really what helped Moore come out ahead. Moore's margin in Prince George's probably would have been weaker had he stayed in and Franchot or Perez would possibly have benefited from that.
Definitely, I won't place any blame on him. He doesn't make the rules and we can't fault him for playing the system as it is and, as you mention, he didn't force anyone else into the race.
My main point is that it is a bit absurd that a candidate can be nominated with a supermajority of voters against him. But this isn't a Moore-specific point and I'd make it no matter which of the many Democrats won.