Glue paint - what is paint and must be removed

In the meantime, the milk paint has been removed, the ceiling has been treated with primer, filled, primer again, …, ultimately a nice result was achieved :)

The renovation continues, the staircase is next, milk paint again, new painter, the same old story: the painter does not want to scrape off, prefers to apply primer, while the paint specialist urgently advises scraping off the milk paint.

In the last four renovated rooms, the milk paint was scraped off, although it was an unpleasant dusty task, the paint was difficult to remove even with water, I tend to insist on removing the milk paint.

Maybe I am too stubborn? Would the professional really scrape off in his own premises or just apply primer?

Washable glue paint is also possible. I have had bad experiences with primer on paint layers containing lime, as it often causes peeling instead of good bonding. I am more "Team Thorough".

Alright, let's assume I were to consider repainting the ceiling with glue paint, this would be absolutely unproblematic, right, or is there any residual risk from the repainting?

As far as the stairwell is painted white, I fear color tone differences between dispersion paint on the wall and glue paint on the ceiling.
Most recently, "Glemalux ELF 1000" was used in my renovated rooms, is there a glue paint with a similarly "clear" white tone?

Which glue paint (manufacturer) is preferable?

Just spoke again with the painting specialist shop I trust: The specialist dealer is uncompromising, the distemper must come off. In practical experience, primer is applied over the distemper, but if the distemper layer is too thick, it might eventually come off. Painting distemper over distemper carries the same risk. Those are the explanations from the specialist dealer.