10 teef is pretty expensive, but no more than a decent big gun. And true a d3 hits is not a d6 hits like a head-on ram, but remember that you take hits too when you ram someone.It's really interesting to see the different opinions on this one!
My line of thinking was that you had to actually try to ram/rake/sideswipe the other vehicle to use the wrecker ball or grabber arm. In terms of multiple arms/balls it could get fairly spammed, although you'd definitely need to dedicate a lot of teef and boys to it (which given the nature of the campaign would allow people to build counter-strategies to it).
I don't think the wrecker ball and grabber arms are inherently over-powered, given they are quite expensive, take significant manoeuvring to use, and realistically only would get used one or two times a game. Even though they penetrate the armour automatically they do less damage than a decent ram, and certainly they are by no means a reliable way of crippling a vehicle (although they do provide amusing effects when you hit the driver or crew!).