-Its price is its counter, you can field 2 squads with that much mp, use that to your advantage.
-If he has the luxury of keeping his arty until you retreat, then you're not pressuring adequately.
-If you are getting a hard time against (this) arty, hold off your commander pick until you see what your opponent picked, so you can counter-pick. It might be 'annoying' to not be able to 'play what you want any time you want' but this is a pvp game, it's not scripted.
This pretty much is the solution.
I remember in Coh1 when I saw double brits going for a heavy arty build I knew I won the game. Since their field presence is just so much weakened by this investment.
Pressure the sh*** out of them, win.
Though I respect OKW problems with base-to-base arty. Its a tough and frustrating ride.