Actually, a light crosswind can actually make it worse. Wingtip vortices move slowly outward away from the departure runway. A light crosswind can effectively hold the upwind vortex on the runway. Not saying that's the case here, but it's something to consider when judging your separation needs.
Dont get me wrong, it does seem like a wake encounter... (eye witness says it banked right first, then left) but it was only an ERJ 135, while the ERJ likely rotated much earlier on the rwy that the A321, it was 2 minutes prior. The wake could have settled just at the ground level, and the 321 got it, but ....
the A321 had problems right at rotation.
ground tracks reveal the aircraft was dragging its left wing tip for quite some distance on the ground, the ground tracks even suggest the aircraft came close to ground loop.
