In reality you have to know the specifics.

And if everyone else is dumping resumes for not having the right tenure lengths, then it is +EV (to use a poker term) for you to keep the cvs on your desk and consider them. You'll get the good hires the others missed :-)

Tenures too short? Maybe they delivered a lot of value in 6 months and were ready for a new challenge. Would you not hire a builder to build your house because they did the last one in 6 months?

Tenures too long? Maybe they had lots of challenges and promotions in their last company. Or they really believed in that company and what they stood for, but had to leave for some genuine reason and now they really believe in you.