No I'm not taking that much of a pay cut, that job doesn't pay enough to waste my time with
More seriously, take a look at the situation at the time. Nill wouldn't sign Tanev for 6 years and 4.5-5 million, knowing he has others to sign down the road, and that Tanev would be 41 when the contract was done. You probably would have trashed that move, as well.
Take a look at the other top UFA d men available last year. Those all signed $6-7Mil over 6-7 years, which would also put the Stars in a bind in the near future. Instead, he signed 3 mid to lower level UFA D men for 1-3 year terms, basically hoping 2 would work out, for $8-7Mil per year and a shorter term. Yes, only Lubs really worked out, but he decided that this type of risk was worth it. And, despite our complaints, they are near the top of GAA average for the league, so it must have worked out okay in total, even if you want to bitch about Dumba having bad metrics.
So, yes, Nill's signing of those three D men is defensible, when you look at it like a GM and try to balance going all in with long term planning. At least, IMHO.