Charging MacBook Pro via dock?

Neither one is, actually. The MBP will draw only as much power as it requires.

It's a fairly complicated implementation of hardware and software, but Apple thinks about these things so you don't have to.

Your Mac is designed to use up to the entire output of the power adapter, AND borrow freely from the battery on a moment-by-moment basis.

The main risk from under-Powering is that you may also depleting the battery when you expect it should be charging. Also, your processor may begin throttling back its performance when the battery gets low.

A rare but possible risk from supplying too little power can occur. You can momentarily overdraw all available power, and the power levels could start to collapse. Inaccurate power levels can be damaging, so this would cause your Mac to do an uncontrolled emergency power-off to save itself.

Using a lesser rated power source won't damage the Mac. It will charge slower and might not even be able to keep up with demand but it won't damage anything.