Haven't played with the Bulldog or Commando yet but the Hydra absolutely filled a new niche and compared to 3 or 4, where there were redundant guns galore or Forerunner versions of UNSC guns respectively, 5 saw a much better sandbox in this respect, imo.
I forgot the Hydra was actually introduced in 5 and would agree it does fill in certain role, so I edited it out of the post initially.
The Bulldog and Commando? If there is only the Bulldog to fill in the role the Mauler did in H3, I will be okay with it, maybe. But the Commando? We already got an SMG for close, AR for close to mid, BR for mid to long and DMR for pure long. And even then, the DMR still kind of conflicts with the BR. Now we got a gun in between the AR and BR? Plus potentially the Carbine or whatever other precision weapon that is coming into the fold? I can't dig it.