Everybody is entitled to look at what's on offer from Jet2 and decide if it suits their personal circumstances or not.
Personally I joined on a fixed term contract as an FO, which was a bit of a risk considering the alternative was a lucrative posting to Qatar, which although financially far superior to Jet2, didn't suit my circumstances (wife and kids settled in uk).
Towards the end of my 6 month summer contract, it became a permanent contract with effect from 1st November, followed a year later by promotion to captain. Initially then, from my perspective, Jet2's offering wasn't great but was grudgingly accepted - however, I'm now on reasonable money, am amassing 737-800 command hours rapidly, and most importantly am in a stable, profitable, expanding uk airline.
Each to their own, and everybody has different requirements and expectations from an employer, but I would just like to point out that dismissing a 70% contract as unacceptable might be a little bit short sighted, considering (as my experience shows) how quickly things change in aviation.