Well, this isn't so much about "aircraft carrier rangers" as it about sheer practicality.
Per the RAW any sudden Fireball and your pet is toast.
This isn't just weak design. It's completely unacceptable design.
The first and foremost design critera for any animal companion feature must be: the pet should not require ressurrection any more often than any other valued party member (which for most groups means "very rarely").
The pet risking death from any random area effect is a bright red line that should never have been crossed and fixing this is essential to the beastmaster subclass, in my opinion.
With "resistance to all damage" the pet's hp total is effectively doubled, which helps a lot with keeping the pet alive in all but the combat-lightest of campaigns.
That the pet might be fragile and needs to be withdrawn from the combat until healed is fine. It is the "death out of nowhere" that means the pet must always be treated like a precious porcelain vase that gets a "hell no" grade.
That the Ranger itself suffers the damage the pet doesn't take is a harsh but fair way of ensuring the errata doesn't just add more hp to the class build.
Zapp
PS. The ward should be strictly one-way. Damage suffered by the Ranger should not affect the pet.
So a Fireball for 44 damage that targets both master and companion will deal the same 88 damage (before saves and resistances) as before the errata, only distributed 22 to the pet and 66 to the Ranger.
Baseline fireball is 8d6 at 3rd level for a 5th level character. Thats avg 28 on failed save and 14 on made save.
So, **if** you choose to keep the companion in the close proximity fireball zone *and* it fails its save *and* you did not support as a group with Aid or temp hp or save bonus effects etc etc etc it can indeed die from the avg failure.
But if it saves, at 5th level ranger, it still has HP left due to the 4hp per ranger level minimum... Right?
An avg 44 hp fireball is what...13 dice... Like 8th level spell or 15th level character so... Whats the minimum HP for the beast then?
Unless you insist on choosing beasts with lousy dex saves that make them more vulnerable to AoE and then make no effort to give them a nudge it seems like your sudden fireball toast is a tad or a smidge overstated?
Meanwhile at 5th level, a ranger with 14 con has avg 44 hp and if we believe that you are actually wanting this to not be about remote/carrier optimization then you want us to believe you want for that 28 pts fireball to be slamming your 44 rangwr to 42 and your 20 pet for 14 so that a slightly above avg roll drops your ranger instead of your pet on your both fail case?
Really, thats what your are sellin'?
Again, this "want" seems clearly focused on or at leadt lets say provides a **lot** of benefit to the remote/carrier ranger style than it does the dynamic duo sidekick side by side style you seem to be painting it as for.
Its also extremely inefficient when you consider 0 hp death saves applyingto the beast.