Knowing Lendl, his philosophy regarding Andy's 2nd serve would be something along the lines of "If you are serving too many 2nd serves, then we need to work on your 1st serve more"
Maybe they feel working on a 2nd serve is a negative mindset, the whole purpose being that your 1st serve percentage is actually much more important.
I still think that comms highlighting his 2nd serve is them basically trying to look for a weakness in his game when there probably isn't one anymore.
I agree with that. The thing with Lendl, it seems to me, is that he doesn't appear to do negativity. I could well see him saying something like that to Andy, making a positive out of a potential negative, if you like. It makes sense as well, get a lot of first serves in, the second serve becomes less of an issue.
I think some of the pundits just like to have something to say to be honest. Makes them look good.