number of gears is not as important as the range of those gears. The only way you could be limited by your gears is if you are spinning out in your top gear and just cant spin faster, but have the strength and energy to do more. If you're spinning out a lot, you could probably just get a new cassette to fix the issue. Most likely, you just need to get stronger.

Having more gears just allows you to pick a gear that lets you pedal at exactly the right cadence you want for any speed. With fewer gears some people might find themselves wishing there were gear in between. I have a 7 speed and a 10 speed bike and don't really find myself wishing for more gears on the 7 speed.