Chally is OP - we know that and it's kind of deliberate as it's designed to be used with the @RAM mod (Real Armor Mod) which modify's weapon penetration levels to simulate real Armour etc.
However my opinion is that Armour overall in the game is too easy to defeat - takes damage to easily and is immobilised by falling branches, leaves and signs put 2 inches out of place on the road. SO for play-ability the Chally is perfect in my opinion. Allows actual reliable Armour support when you need it.
The argument over whether it's defeat-able is not accurate in my opinion. as Zeus I've killed it and it's crew LOADS of times either in Leopard 2's - using Helicopters or with ATGM (ok lots of ATGMs

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Now Mines MAY not have been configured properly - I have no experience - equally Chally 2 may not have it's Lower Armour modeled accurately to simulate Mine hits ? no idea. BUT I think surviving 3 IEDs isn't un-realistic - after all the only real Chally 2 kill was a Blue on blue... (

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SJ