Not necessarily. Two things at play here
1) If leg stump guard, you have easy access to ball on middle and off stump lines (as pads out of the way), so you play with bat more often for balls on the stumps line
2) If the ball is angling in and impact on leg stump line, then high chance it might be going down leg versus impact on middle or off
If it's going down leg, it's going down leg. I said if the ball was straight.
I would say one of the benefits of off/middle and off is probably that you can get your pad outside the line to the ball jagging back in to hit the stumps.
Another thing I've heard is that players have realised they were triggering to get onto off-stump, so have thought why no just start there?
But I'm not a fan, and I understand the accessing the ball / not 'closing yourself off' arguments.