Badniks in Sonic games always start out fairly easy (the Motobug in Greenhill for instance just goes back and forth).
Though back when SRB2 as a project was just starting, I would think that the Crawla's logic was fairly easy to code given the state of the engine (just the Chase action from Doom for the most part). There was no Lua API or even SOC to make the work easier.
Today, it is one of the game's iconic enemies and is widely regarded as modders as a key unit type for Robotnik's army (hence why you see so many custom variants).