Business sense yes.
something that so many pilots seem to think they are so good at that they constantly complain about how poorly their airlines are being run!
But let’s see them run any type of business that invests significant resources in training a particular skill set that is valued in a market and then see that INVESTMENT immediately leave your company for other opportunities.

employment contracts are everywhere. One of the biggest is call the UNITED STATES MILITARY! :-)

If they are transparent then there is nothing wrong with them at all.
the prospective employee knows about it and knows what he has to do to get out of it by staying or paying a agreed upon (hopefully pro-rated portion) should he decide that another opportunity is worth it.