Slacker head tube angles typically make for a less responsive bike; but this isnt a good or bad thing since the question is whether or not the overall design is balanced in terms of feedback to actual turning action. One of the concrete benefits of the slacker HT angle is increased front-center and wheelbase for larger riders without increasing reach. Because of current forward trend in bike fitting this has meant that in turns there is too much front weight bias giving bikes a tendency step out.
My opinion would be that they should just increase reach by 2-3% across sizes and call it a day rather than slack out the HT angles, but that creates fit problems for many riders and then you are fighting decades of bike fitting "science" and aesthetic.
bolded part is all industry marketing mumbo jumbo. second part is true, but the main thing is about reducing deflection of the front wheel due to riding surface, wind, or manhandling the bike at high power out of the saddle and increasing stability at speed. taller, heavier riders need this more, not less than smaller riders.
increasing reach (and thus FC) will only increase stability a bit - as it'll be a smaller amount and head angles would still be far too steep.
from a fit, bike handling and geometry perspective there is absolutely no reason for larger frames to have steeper head angles. whilst there's plenty for them to have slacker head angles. the status quo is purely about package size.
also any further increases in reach are going to need increases in seat angle - they're already far too slack in larger sizes.
