Sure it increases the power. You essentially grant a reaction to further insulate a wizard from taking concentration checks for example (far more valuable than preventing damage to the monk). Not all targets are created equal. Further to that, or perhaps more generally, the monk ability only works on himself, whereas with range you are preventing damage far more generally and more often than in just cases where the monk is targeted. It's not that the ability itself is better, more than there are significantly more available occasions to use the ability, which I submit does make it more powerful.
A case that would mitigate the above is if the reaction slot for the Marshal ends up being crowded and he's forced to make meaningful decisions on a turn by turn basis about how best to use that part of his action economy.
A case that would mitigate the above is if the reaction slot for the Marshal ends up being crowded and he's forced to make meaningful decisions on a turn by turn basis about how best to use that part of his action economy.