I believe these issues go a bit deeper than simply having external Jet Pilots from other carriers getting the jobs in Air NZ instead of the Link Pilots. If it were as simple as that then it would have ruffled a few Link Pilots feathers but we wouldn't have seen the retention issues that has been experienced over the last 3-4 years.
The first problem was the decision to close the regional bases. We saw the Napier Q300 base closed with forced moves for all involved, the remaining regional bases were all told "you're on borrowed time and will be next".
The only bases on offer for all new hires, and new commands was AKL,WLG and if you were lucky CHC. That was it.
The second problem was the introduction of the new schedule in the later part of 2016 which instantly saw time away from base skyrocket. Some Pilots were doing 280-300 hours every 28 days capture time and going away for 2-3 nights at a time. Due to the scaling back of all regional bases through natural attrition allot of the overnights were in places where there was a base.
The expansion of Mount Cook and the Jet fleet simultaneously meant that there was no choice but to take external Jet Pilots from other operators. This created a situation where there was no negative effect to leave the Links - better pay which was important for the main cities, better lifestyle and probably a quicker route to Air NZ Jet anyway.
The merger and the reintroduction of regional bases is definitely a good thing, but it think it needs to go a step further. Open up regional bases in more places similar to the old Eagle footprint, this will allow Pilots to live pretty much anywhere (within reason), the more career driven ones will naturally take commands in the less desirable bases and move onto the Jets sooner, the lifestylers will stay in the regions and wait for their command there.
More bases means less overnights and more day duties which reduces the time away from home for everyone. Keep the 1 year Left seat requirement to qualify for Tag and Release on the Jet Fleet. Do that and you will ensure even number 600 on the list will probably stay, because if someone way down the list gets a quick command in a main centre then you'll find they won't be number 600 in line for a Jet job as they will jump all the ones choosing a lifestyle base over career progression.