The problem with the JoAT is the three words that are supposed to follow, of course- master of none.
Even if "all the bases" are covered in your group, there are always roles that can use redundancy (really any role). If you have a heavy combat table (or even a rp/combat balanced-table), a different take on a combatant (melee? concealable? explosives/heavy-gunner?) will always play well, especially cuz you can always tack something else onto a combatant (B&E? medic?). Facing, no matter the table-type, is also so handy that it can never hurt (indeed it can be a tremendous advantage) to have 2 of them. Not sure how easy it is to do back-up decking in 5E (assuming that's what you're playing) and still have resources for something else, but that's also a great advantage to a group - one guy running group-tech cover/offense, one dealing with security systems, drones, etc. Mages can be sooo diverse that you'll always have something to do, summoning, buffing, debuffing, face-melting. Basically, every PC type is diverse enough, or capable of being diverse enough, that redundancy in any of the main roles is just fine. You'll be more effective and probably have more fun just playing something that interests you and is more capable at those 2 or 3 things.