Venom is a great champ especially for variant content. He has very solid reliable damage and utility. There are no cons in r3ing venom as getting Hercules could take a few days or 2+ years and if it does take awhile you are likely to be close to/have another t5 cosmic catalyst and at that point you can also r3 herc.
Do it! Venom is so useful through out the game. He was my first r3 Cosmic. You'll eventually have multiple r3 of each class. No need to wait to rank a great champ.
Comments
I personally think Venom is Overrated