We are also thinking in old paradigms here.
It used to be that getting a fusion blaster within 9 inches, beating the target's AV and then rolling a 5+ on the damage chart was our best way to kill high AV vehicles.
In 8th Ed, high toughness, high wounds models are the targets of the fusion blaster. These targets will not be destroyed by a single lucky hit, but instead will go down to the weight of repeated hits depleting their wound pool. So the roll twice and pick higher result, while a nice boost, isn't essential to the working of the fusion blaster as being able to roll 2D6 for penetration was.
Also, the Fusion Blaster isn't going to be the only way to reliably injure those high end models any more. Heavy Rail Rifles (baring some unexpected special rule or nerf) are going to be just as likely to successfully wound targets as fusion blasters. Against most former vehicles Ion Cannons and Ion Accelerators are probably going to be as deadly as Fusion Blasters (if not more due to the way the blast rule now works). The HYMP and Missile Pod are also likely to be no slouch at putting a lot of wounds on things they couldn't even hurt under the AV system.
So the sky isn't falling. Instead we're seeing something we haven't seen from T'au for years. Anti-vehicle capability distributed across our army, instead of clustered in suicide crisis suits.
Honestly, I think the go to Crisis Suit weapons this edition will be Burst Cannon, Plasma Rifle and Cyclic Ion Blaster.