Thing is, the material is somewhat irrelevant to us, the end users.
The frame components of a full sus need to be stiff enough to tie the various mounting points together without flex compromising the bikes performance, and it needs to be tough enough to survive the usage it's likely to be put through over a reasonable lifespan. How it's achieved is the bike designers problem. We're only interested in how the finished product rides.
For an abuse friendly 150mm bike, there seems to be relatively little difference in weight between steel and ally frames, not so sure about carbon stuff thats appropriately stoutly constructed, rather than built to be superlight. Also bear in mind that on a slack 150mm bike, wheels and tyres (and other components) need to be relatively strong to cope with the kind of riding that kind of bike encourages. A few g +/- on the frame is irrelevant.
I've spent about 10 hours on a Rocket (and only the chain stay and droplink are ally, the front triangle and the seatstay are steel). One of the least relevant things about it is the frame material. It's way stiffer than my Uzzi. It handles beautifully and it munches technical climbs for breakfast. The demo bike was 5lb lighter than my Uzzi (which is as light as I can get it without compromising performance). About the only relevance the frame material has that I can think of is that the downtube is slightly less likely to get covered in dinks from rock strikes.