The only two drawbacks of leaf blowers are:
1. that they're a rather large and relatively heavy instrument, and because of that you're always risking hitting the paint with them, and inflicting some physical damage to it, and
2. that there's also the chance that a leaf blower will suck in something it shouldn't, and throw it at the paint, again, possibly causing damage in it, and also in whatever it sucked in (for ex. parts of your clothing).
Both of these accidents happening will be virtually impossible if you're using a dedicated car dryer, which has its motor and most of its weight stationary standing, and is equipped with appropriate filters.
However, other than those I see no point in using a dedicate dryer, and honestly, IMO they're so overpriced, that unless you're doing car washing professionally and/or on very expensive vehicles, it just makes no sense to invest into them. Because it's not like they'd be actually better at blowing air than a high performance leaf blower.
Anything that would give you a real advantage over a leaf blower in precision, convenience and minimizing damage risk would be something very, very expensive: a system where you'd have automatically retracting compressed air tubes hanging from the ceiling, and you'd just attach the blower heads to those to go around the car with that. Such a system of course could also be used to drive pneumatic polishers and some other detailing stuff... but as said, such an installation would be very, very expensive, and out of reach even for most professional detailers.