Got a Real World Weapons or Armour Question? Mk XI

[Raum]

Finally, if militia could could be on par with mercenaries, why would Venice -- who are generally agreed to have some of the best trained militia -- have hired mercenary infantry on long term contracts?

There are lots of potential reasons to use mercenaries - you may not want to risk your own citizens, you may simply not be able to afford the economic cost of having a large portion of your work force gone for an extended period, you may not have one or more specialty troops (cavalry, siege engineers, etc), or you may simply need more troops than you have.

On the flip side, permanent professional armies have almost always been better than militia. It's the difference between making a living at something and doing it part time.

I don't know the era well enough to have a strong opinion on which may have been better - but even if they were equal they might still have hired mercenaries.