The development of our brain reduces the amount of muscle, hairs
(arguable) and senses.
That is a remarkable mixed bag in one sentence.
1) Muscle: No, the metabolic demands of the brain have nothing to do with the amount of muscle we possess. If it comes to that, nobody is quite sure why we are (relative to chimps, for instance) weak. It seems likely that Neandertals were very strong, and apparently we wiped them out. So it's clear that, for one reason or another, beyond our current limits more muscle simply doesn't help survival all that much. The existence of freakishly strong people shows what the human genotype is capable of, and such people do not seem to be short-lived the way, for instance, super-tall people with an excess of HGH are. It's just that it doesn't do much good to be super-strong in a world of tool-users.
2) Hair. Oh, hell no. The metabolic load for growing hair is simply not an issue. After all, if hair follicles produce long-lived hair, the total effect will be more hair and a shorter replacement rate will work. Rather, it's an issue of heat management, and we seem to be adapted to be long-distance runners in a hot climate. More body hair and our deep ancestors would have been in deep trouble.
3) Senses. Now there you're on to something. Sort of. But probably not really. A large chunk of our brain is devoted to visual processing. In the process, we've lost (if we had it) a lot of smell-oriented abilities, although we also don't have an enormous number of scent receptors, either. Dogs, for instance, have an enormous suite of receptors. And their vision is not great. However, much of what people think of as "limited" abilities in our senses are partly due to the fact that most of us simply don't need to pay that much attention to our senses, other than sight. Our hearing is actually quite good, although the limited size of our ears is a limit. And note that some issues require other specializations. Some owls, for instance, have superb auditory location ability (good for hunting in the dark) - but their ear anatomy is asymmetrical to help the process. We don't have the long-distance vision of raptors, but the eye anatomy which produces that vision would be pretty useless - we don't need to spot mice at 100 meters, and we do need to be able both to see fine detail up close and have decent peripheral vision. And some people have much more discerning taste abilities than most.
It's true that if less of our brains were devoted to "cognition" (whatever that is), we'd have more to spare for sensory processing, but it's not clear that that would actually help much, so it doesn't happen. Note that other species would seem to be able to perform better with better senses, but they don't grow bigger brains to allow it. Apparently, there is a point of diminishing returns on sensory processing. What we did was to invest our resources in a different sort of processing, and that made such a big difference that it allowed for larger brains to survive.
Of course, there is a certain chicken-and-egg issue here, and the subject of exactly why our brains got big in the first place is the subject of long-standing, sometime acrimonious, and certainly inconclusive debate.