You have a signal chain, from your fingers to the cone. Every bit counts towards the final sound. And then you have the audience and the room. All your gear should be good, but the cabs do the heavy lifting and they should be the best you can afford.
The rule of thumb in the old hi-fi days was to spend 50% of your budget on the speakers. That's how important cabs are to your final sound. Cabs are still important if you are DIing, then its the PA cabs and your monitors that are critical.