At the moment, native max packing can't be used for anything apart from quick tests and prototypes. It wastes too much space. Preparing UV2 for lightmap is a pain without third-party solutions. Best what I've seen from competition is UVPackMaster (can you buy them please?). It can do pretty much anything you may want from UV packer.
Notable features that are currently missing or lacking in 3dsmax implementation:
- coverage percentage is shown
- automatic stacking of similar elements and locking existing stacks
- filling existing layout with additional elements, say you want to add a bunch of tiny elements into existing unwrap without moving elements that are already there
- better grouped distribution, grouped elements can try to stay together, not just be treated as a single shell, but for example fill topmost third of UV space with group 1, middle is group 2 and bottom is group 3. Distribution is not limited to this layered stripes of different groups, it is just a simplest example
- separate margin and padding (shell-to-shell and shell-to-border distances can be different)
- and most important imho is iterative (heuristic) packing, which will endlessly search for better solution, updating unwrap when better-than-current is found. Combined with its flexibility in general (adjustable precision, allowed rotation angle step etc) it can provide very accurate and tight packing with minimal UV space loss
and those are just ones I used. I think it can also pack into UDIMs among other features, but didn't tried it personally.
This part of UnwrapUVW didn't change much for decades, I believe it's about time to give it some TLC.
