No cutting required. I removed these kind of dents from my vintage tweeters. Take carpenters white masking tape. carefully lay over that dent and with small pressure, not increasing dent, press against dent. Make sure it sticks well. It make concave shape leaving 1" longer tape both sides of dent to pull.
Pull masking tape making 45 degree angle to tweeter surface and tape. You are done. Don't worry you can repeat the process, no damage is done to tweeter.
Dont make any hole into cone. Vacuum did not work for me.