Part of me thinks they should have gone with different builds like tank, dps, or control with a modifier for creature type. I guess that's what the elemental beasts are somewhat trying to rectify.
For hit points, I think they should have gained extra hit points and a commensurate number of hit dice which would allow constitution bonuses (and, I guess, penalties) to be applied. It would also provide them with the ability to heal up during short rests.
They really should have taken a hint from 4e and had multiple templates for your beast based on the 4e monster roles.
Or if they wanted to save page space, just let you take a specialty training for your companion. If pokemon trainers can do it...
I mean that's the difference between rangers and druids. Rangers are humanoids and are willing to use methods unnatural to get it done.
BRB feeding my bear a diet of HP UP and Protein for +2 HP per ranger level and +2 to attack rolls.