Yes, Behemoth won't be effective day low-damage output, but he already has too much health to tank the low-end damage.
Hunters like Slim, Hank, and Torvald were the ones destroying him.
Now, even with those hunters Behemoth can tank the relay with majority of his health. He's the same tanky S3 monster like any other monster, so his S3 damage is high enough to easily tear through the hunters.
Instead of a passive to counter high burst damage characters, he needed more mobility in exchange for less health, but regens more health during evolution.
Otherwise there is no incentive to fight until S3. Especially on large cave maps like Distillery or Weather Control, where "baiting him out" and "waiting him out" is simply not an option.
Waiting him out gaurentees he gets free evolutions, while fighting him in his home turf is suicidal, not to mention any Hunter with Deployables is easily countered. Because he gets free evolutions, he reaches S3 with near-max health, and let's be real, does any decent monster lose to the time running out on a relay where they have almost full health?
All on top of that, the dropship for FT3 is 1:10 if I'm not mistaken. Then the first down adds 10 or so more seconds to that time, and because they are dead, assuming it's support or medic the rest of the team cannot outplay a S3 monster for 1:20. Nor can they kill him in one dome.
This is why I hate Behemoth. It's never a game like Goliath where you can have clutch comebacks as both him and/or the hunters.
This is why I dislike the passives. It's giving a tank more armor when it was never the problem in the first place; it was his mobility or lack-thereof, causing him to be easily countered by said hunters.
I'd like to tack on the fact that now Laz, and any class with deployables is countered by Behemoth. Talk about a hard counter.