Bogging down can be a sign of needing a hotter plug, but only after you're sure everything else is just right. No leaks. Right prop. Right fuel. Tuned right.
BigEd has a good point. I don't use the pinch test. I let the engine idle about 30 seconds and then advance the throttle. If it is tuned well enough to take a normal increase I'll see how fast I can stomp on the gas. I'm looking for how much the crankcase is loading up with too much fuel (too rich low speed needle setting) and how well the plug burns it up. Every engine is different.