Weight is dependent on the intended usage for the machine. My 120/130 xc/trail bike weighs 28lbs, my 170mm enduro race bike/park bike weighs 36lbs and my rise weighs 45lbs. Quite frankly, the weight of each bike is not what I notice when I'm riding them and each of them weighs appropriately for their intended usage. I wouldn't want my trail bike to be any heavier then it is and in contrast, I wouldn't want my enduro bike to be any lighter then it is. The weight of my enduro sled keeps it stable at mach chicken speeds. It uses double down tires, cushcore and coil suspension front and rear. As a result, it is incredibly confidence inspiring at speed and doesn't flinch at all when I come up short or make bad life choices on it. Interestingly, my enduro sled rides almost exactly like my rise with a 10lb difference. The only time I notice the weight difference, is when I'm loading the bike up, or I'm trying to bunny hop a log at a walking pace.
Ultimately, weight settles the machine and provided it's un-sprung weight, it can actually improve suspension performance in some aspects. I digress, in certain circumstances, lighter is better for sure... but there are limits. I absolutely wouldn't want my rise to be any lighter if it means less capable tires, less stout rims, or less suspension performance. That would be one of many reasons, it would be worth it to take the 1.5lb hit to run a 36/floatX instead of a 34 and dps.
One last comment... A 24oz/700ml water bottle weighs 1.5lbs/.7kg. I am incredibly sensitive to bike setup, more so then most anyone I ride with regularly. There is absolutely no way, I can tell the difference in how my bike rides with a full water bottle vs none. To that point, no... 1kg of sprung mass, does not make a difference to how a bike rides.