My response was originally to epochrpg's post in which he stated that a ranger's companion should be durable. The only way to get that sort of idea is if that had been the case in the past, otherwise we wouldn't have any notion of what animal companions should be like. Therefore, I responded by saying that the companions are just as tough as they have always been, countering his point. This is perfectly relevant to the OP's title "Can it survive for 2 rounds?" which, yes, indeed it can.
However, I note that you have not responded to any of the other points that I posted. Therefore, I have to assume you have nothing else to discuss, and wish to continue nitpicking for the sake of nitpicking. I will not respond to that again, so have a good day.
The 4e companions were much better than 5e and I'm not exactly a huge fan of 4e. In other editions, you could
get better companions as you leveled (I'd take a wolf, and when I could get a dire wolf say it grew up, so it
was the same pet the whole time).
That said, who said it has to be compared to another edition? The section on mounts gave
griffins as an example; there is no class feature to have a pet griffin (except 3.0 may have allowed this in a
splat book for paladins). The character concept demands the pet live for more than 2 game sessions in a row
while still getting to play an active role. It cannot do that with 4hp per level and no decent saves.
My own experience was in DnD Rules Cyclopedia that the GM house-ruled to allow GURPS Ads and Disads
(this was quite a long while ago, as you may imagine). But by this method, I had a pet dire-wolf
at 5th level. In 3e and 4e, it was possible to re-create this character. In 5e, it is impossible to ever
get a dire-wolf as a ranger's companion. You have to go druid, and then devote a spell slot to casting "animal friendship' on it every day, until you can finally cast Awaken on it.
An Awakened animal is also better in every conceivable way. Not only can it think for itself
and defend itself, it can do this when you have a horrible DM in league play who insists on being
a complete rules lawyer. Mearls can tweet that a companion can do this all he wants; until it is in the rules,
there will be DMs out there, especially in league play that will ignore the "just use common sense" tweet
and use the RAW, which says the opposite (it says the pet sits there an does nothing unless you spend an
action; the GM can reskin this as it snarling and dodging till he is blue in the face, but in mechanics,
the animal sits there and does nothing).
