To begin with, hats off to Doborog for outdoing themselves yet again with this most recent edition, which has not only an impressive design, but unique mechanics and smooth animations.
That being said, after having not played the game for a couple weeks, I just booted it up today and shortly thereafter beat the Raptor Insanity challenge in a single go. Immediately after seeing the Raptor's attacks in the first round, my first thought was "bow". I was not wrong, it seems, because the rest of the challenge was largely trivial; it appears the new enemy is entirely invalidated by range. Not only does it frequently "die" from a single arrow hit (presumably due to its large, long head and the arrow's penetrating capabilities), but it doesn't (that I've noticed) possess the side-to-side random motion of Mk3 units (specifically the Hammer Bots) that allow them at least some protection from sniping. At the same time, however, the bow seems to have precious little usefulness in normal play (being, in my opinion, thoroughly outclassed by the reliability, rapidity, and protection of the sword), so having a relatively dangerous enemy that's only effectively countered with it is a great incentive to use it.
Simultaneously, however, and this is just my opinion, I'd prefer it to be an intimidating opponent (its model and size just scream "I'm going to ruin your day"), rather than a relatively high-priority removable obstacle. A couple simple (not necessarily so to implement) methods of fixing this subjective issue would be to armor it so multiple arrows in the same location are required to down it (which would, I think, be pretty interesting), and/or alter its AI to make it more difficult to hit. What do you think?