I honestly believe the comparison as to whether the pain is severe or not depends on the person.

One lady I used to bind had boobs you could use a paddle on, and she hardly noticed.

My current partner is so sensitive, mere nipple stimulation can drive her to multiple orgasms. I don't dare use anything forceful, nor can we go to the well-known 'balloon tits' ties; the first time we tried, she used her safeword after less than 5 minutes, and the pain lasted a few weeks.

As with all human endeavor, communications and caring are the keys to success.