Spikes coming out of our heads: Why?

Giant Fangs: Our common ancestor had to transition to Omnivore in order to obtain lots more food. Having giant fangs would fuck that up.

Spray Acid: Giant trade-off when having to spend more energy creating that acid. Sure we could spew HCl on our prey or predators, but not when it could give us less food to eat by spewing acid on them or costing us more calories to sustain us.

Nah, humans are pretty cool with what we got. We have the cool ability to outpace most animals in that we can just chase animals around, get them tired, then eat them, even if they ran thrice as fast as us. Wolves hunt the same way. We can throw shit and accurately too. Found a good rock and need to disorient a deer? Chuck that sonofabitch at the poor bastard. we have the biggest dicks in the primate family we have the biggest brain case ratio of all animals, which is kinda how we're even clever enough to discuss this stuff.

There are so many different varieties of dogs because of selective breeding.

Doing that sort of thing with humans tends to be frowned upon by the international community.