It makes sense to me, too. But I think the factor of staying as true to conventional Magic rules outweighs the (slight) gameplay benefit which might be achieved with your proposed rules change.
I would rather opt for a total return to the core and just go with the normal mulligan (abandoning the free mulligan altogether).
I would rather opt for a total return to the core and just go with the normal mulligan (abandoning the free mulligan altogether).