The problem on Crossroads isn't really that they can't be countered, it is mostly the fact that there are very few obstacles in front of GDI base and it's rather easy to setup Arties almost in any location and snipe from the elevated crossroad (on Field there is at least a cliff protecting half of the base). A bunch of guarded Arties can kill the GDI base in a relatively easy way, as It also takes some time for GDI to mobilize and get there, and once again Jump Jets, the usual counter measure against Artillery no longer works.