By your own admission, you haven't watched a lot of our games this season, so how you can pontificate that Verms has been our best defender is beyond belief.
Koscielny has been our stand out defender this year, assisted by some good performances (and some bad ones) from Verms and Merts. Verms has cost us two goals in the last three conceeded, one own goal, and a bad pass last night. Merts has had some wobblys, but has made us more assured from set-pieces. Kos has read the game better than any other, and has bailed us out of shit loads of trouble.
Problem is, if you only watch MOTD, you're only gonna see the goals, and not all the good stuff he does.
They've all fucked up in some way shape or form, but defenders are usually at fault for goals conceded. In any match, in most goals conceeded.
Point of fact is, we're not shipping many since our "rejuvination". And that is down to better defending all round. Which I'm sure we're all pleased with.