[meheleventyone]

"She's getting paid based on years of working experience and those 16 months can't count towards it of course."

This is basically an arbitrary choice, you're still paying their salary so why not continue everything else? Similarly a male engineer might want to take 16 months paternity leave.

Allowing 16 month long full-paid leave for new parents would be an amazing policy though. This also seems like an issue with this example as IME there are very, very few companies this generous.

[throwawayosiu1]

We are paying salary as a perk. Legally we don't have to.

With that in mind, why should those 16 months count to experience?

Work was not done by said engineer, and experience was not gained.

The other engineer worked, gained experience that's valuable to the company -> hence the raise + promotion.

[meheleventyone]

Well you don't have to, it's a perk just as you don't have to pay their salary. Which is why the distinction is pretty arbitrary. And experience isn't the only reason to keep up pay level for example you want to remain competitive with the local market and inflation. Presumably you also value this engineer and want them to come back to the company rather than find a new one with better pay if they feel they are falling behind whilst on leave.

You could also make an argument about the gain in experience due to motherhood and being able to take an extended break from work. I believe I'm a stronger developer for having two children for example.