We're starting to see the current FOB gameplay become unsustainable with the counters now available and that's OK

The game started out with infantry battles because nobody had level 3 hammers, helicopters, or artillery tanks. Then everybody acquired the tools they needed to live peacefully in FOBs and build drills. From your base you can find the enemy base that's shelling you and shell them back and this allowed the FOBs to continue. This even led to the hot zone being vacant in some games or only casually held by one team the whole match. Now that artillery tanks and attack helicopters exist drill FOBs cannot easily defend against all types of incoming attacks with legacy strategies. This makes setting up a FOB early and playing how some have become accustomed to frustrating but all of the earlier progressions to team strategies were equally as frustrating. The play style and the counters will evolve over time and while changes are difficult to address at first the teams responses to these issues will continue to become more refined easing those concerns in the long run.

Right now someone can buy a $6k chopper (an SUV also works) some c4 or IEDs and hunt down artillery tanks. It's cheap and available at early levels. The artillery tanks cannot hear anything while they're shelling so use that to your advantage. Then there's the obvious expensive drone counter which can be launched from almost anywhere on the map with enough mechanical supplies.

I would also suggest having a mobile AA strike force that fills a vehicle with AA launchers, and find unique ways to make flying a (attack) helicopter unsustainable. This is a counter that also doesn't break that bank.

Once enough of the community is aware of these counters a few builders can continue living in blissful ignorance of the front line until the next evolution in warfare makes everyone cry on reddit again.

A side note about armor: the more spent on a loadout should equate to more survivability. Yes, lower tiered loadouts will have a more difficult time countering these players, but they lose more when you kill them, and you lose less when you die. The difference in time to kill a tier 2 vs tier 4 armored guy with an AK and the standard FMJ ammunition to the chest is less than half a second and two attackers negate the advantage. Work together, and move in cover, your kit doesn't matter as much as you would like it to.