Yes, the prongs on the freewheel removers are very hard and delicate. Smashing the wrench with anything could snap the remover and gouge out parts of the freewheel, making removal impossible.
Better to use steady and increasing pressure on the remover. Most of the time, clamping it in a vice would be fine, but I've had freewheels that were so tightly stuck that I've broken vices and bench-tops trying that. Easiest to use a longer lever than the rim (big wrench). And use your weight to apply the force. Aim the wheel so it spins into something stationary and step on the wrench:
