I've only bothered to cap 6 jobs. My merits are entirely focused on 2 of them. However, I'm completely still able to use the other 4 jobs in content. So, personally, I don't see the problem. You don't need the club or staff ws to play the jobs that use those weapons, you don't need all your merits in HP to be able to play a tank, you don't need all your attributes in INT to play your BLM.
The whole premise of the merit system was to give your favorite jobs a boost, not to lock you out of playing other jobs (and it doesn't).