Okay, im going to ask this again, and without answer im just going to assume You are just trolls, or You are intentionally ignoring anythig that is not fitting Your complainings.
Not because i feel i know better, but because im trying to explain to You my line of though, and when You will understand it You can then tell me where my logic were broken, or agree with me. It is impossible to tell anyone that they are wrong without understanding their point of view.
I'll join in. I hope I can explain this clearly enough to convince you of the contradictory opinion, or at least that my detailed explanation will convince you that I am speaking in good-faith and not trying to antagonize people for fun.
It's interesting to try to explain the key mechanical and thematic difference between growth and emigration in old and new Stellaris. The 2.7.2 system of pop growth and migration does have potential for simplicity and avoiding leaving buildings empty (as there will be no pop decline under most conditions) but there are issues that make it hard to fully replicate what we had before in 1.9.1 migration.
If a pop declines in one place and a pop appears in another then one way of explaining it is that the pop moved, that's a perfectly valid interpretation of the mechanic - but only if the two pops are identical, and the exchange of pops is synchronous (True in 1.9.1, False in 2.7.2), if the two pops differ in any way, or arrive before they leave, then true migration has not happened.
If I leave my house tomorrow (emigrate) and a Blorg moves into a house in another city (immigrate) one week ago - I have not migrated to the new city, the Blorg who occupies the new house is a new person. Different. Distinct. Also clearly not me, or even human. No idea where I've gone. I've disappeared.
The 1.9.1 system could have a Blorg, a Human, and a Fox all migrate from 3 different planets to one planet at the same time. These 3 pops would all leave and arrive at the same moment, with a modifier saying they've recently moved, and be a little happier for a time while they settle in. All those pops that moved keep their species, traits and ethics - they are the same pops that have moved. It makes sense to say that because:
1. 3 Pops physically moved, they left behind holes and filled spots on the new world
2. The 3 pops already existed, to move requires you exist first
3. The 3 pops are the same species they were before the move (moving doesn't genetically modify you)
4. The 3 pops kept all the traits and ethics they had (moving doesn't delete information or make people pacifists, declining a pop deletes pop information)
5. The 3 pops have a "migrated" marker boosting happiness (migrating pops are clearly marked and easy to see).
6. The 3 pops could stop migrating at any time (if conditions change, moving to a different world or staying at home)
7. The 3 pops stopped existing in one location at the same time they started existing at another (no gaps, no existing at 2 places at once)
In 2.7.2 system pops can "move" (emigrate) from the Blorg planet, the Human planet and the Fox planet. All 3 planets lose growth, and if overcrowded they also decline, and a max of 5 points of growth is added to the new planet (some will probably be lost). 3 new pops are generated in due time, the first new pop is created before any have declined. These new pops will be whatever is picked by the pop growing system - e.g. Cockroaches (say it's a tomb world). Now it makes no sense to say that 3 pops have migrated here because:
1. No existing pops have moved
2. The 3 new pops are new
3. The 3 new pops are a new, different species
4. The 3 new pops have new, different ethics and traits
5. The 3 new pops are functionally identical to all other grown pops, they don't have any "migrated" marker
6. The 3 planets could "migrate" 0.9 of a pop, then stop declining before a pop is removed (e.g. build more housing). No pops disappear, 2.7 pops appear elsewhere from emigration. Decline as a mechanic very rarely happens except under extreme conditions.
7. Even when pops are declining, the new pops were created before any pop declines (growth+emigration is faster than decline).
If you compare the 2 systems then obviously 2.7.2 has merits if you removed the bugs. Simple, automatic, no pops actually move. This stops the pop numbers from declining and reducing jobs by ruining buildings by dropping below the building thresholds. But it has bugs, flaws and the 1.9.1 system could fix this with only 1 added check.
Bugs in 2.7.2 Emigration:
1. The cap on emigration deleting growth above 5 (why a cap? why so ridiculously low?)
2. Stopping and starting pop-growth/decline deletes the progress (e.g. employing and unemploying a robotisist resets robotic pop growth, ditto for automatically changing pop templates when it flickers to no pop growing for a month for organic templates, even changing the growing pop deletes a proportion of existing growth and ongoing growth - not sure what happens to the 100,000+ people out of however many individuals that one pop represents)
3. Declare Population Controls is supposed to add "+100 Emigration Push", sadly that has no effect because Emigration push is multiplied by 0 thanks to the −100% Pop Growth, 100x0=0. The -5 Stability is just icing on the cake made of poo. Fix it so that it causes 100% of growth to be added to emigration and for pops to simply not grow on the planet (without setting the value that emigration needs to work to 0). Remove the stability loss. Similar changes are needed for the 3 other decisions, none of which transfer pop growth to other worlds automatically. This design oversight is most of the problem, and encourages manual resettlement to transfer growth from planet-to-planet, forcing manual migration because the migration system is broken.
But the 1.9.1 system of automatic migration could work if one simple, additional check was made (beyond what already has been coded):
1. Do not resettle a pop if moving it would lower the jobs on a planet:
Dropping below a building-slot threshold (every 5 jobs up to 75 jobs by default)
Below the extra merchant threshold (Merchant job per 50 pops)
Below the portal researcher threshold (per 40 pops), (Gas Plant Engineer per 20 pops), (Subterranean Liaison Officer Job per 20 Pops), (Cave Cleaner Job per 20 pops),
Below the Gestalt threshold (Synapse Drone Job per 20 Pops), (Maintenance Drone Job per 20 Pops)
Specifically the 1.9.1 system would work if you code it to not allow pops to migrate if it would reduce the planet below the following pop counts:
5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 100, 120, 140, 150, 160, 180, 200, 220, 240, 250, 260, 280, 300... and so on.
(you can remove the 75 pop threshold for those that have the adaptability tradition that adds 1 free building slot per planet as the last building threshold no longer opens a new build slot. This list of thresholds would only need to be updated when a new feature is added that adds scaling jobs in multiples of anything other than 20 or 50.)
I hope that helps clarify why migration in 1.9.1 is completely different than bonus growth from emigration in 2.7.2. And how the 1.9.1 system could easily be reintroduced.