It's pretty massive given that those are mostly fighters on the downslope and none were stars. You don't see champions, the most valuable fighters, being able to shop around their services.
So instead of having the UFC pay fighters more, you'd rather those fighters work 9-5 jobs and not amuse us? And you're a fight fan, correct...?
And if that market is dysfunctional and dominated by a company with nearly unheard of levels of monopsony power and market concentration? Healthy competitive markets don't magically spring forth without regulation, and mma, just like boxing, is an industry that is more prone to abuse than most.
Said engineer would also not be banned from doing related contract work on their own time, nor would they be frozen out of their career for 3 or 4 years if they want to shop around for a new employer after finishing their contract. Not to mention, in your silly example, if the employer really liked their engineer and he finished a job, he would be required to keep working for them (champion's clause).