I think Kirby was just being positive about the fact that such a massive discussion was going on.
In terms of increasing the weapon variety to increase the gameplay variety. It makes sense that the meta would eventually settle down, and that weapons could be balanced internally. But there's something of an opposing force to that, which is that more strategic weight would be placed on your team's build. This obviously seems to be a positive thing for Robin, but I feel uneasy about it, because at the extreme it would reduce TF2 to a battle of builds, where at the moment it's a battle of execution with just a touch of builds (I think someone said this earlier?? Can't remember who sorry).
I feel that every time you increase the materials that you work with, it inserts some randomness into the game. You can kind of see it between 6s and HL already - it's much harder to coordinate 9 players than 6 cohesively (imagine it with 100 unlocks as well), and this can lower the skill ceiling in some cases. Often builds and strategy would be more effective not due to any design but just by coincidence.
This would all be avoidable obviously, I'm just saying what I think the potential danger is, and why I prefer strategic weight on positioning/teamwork etc rather than builds.
EDIT: And if you think of balance as [success being representative of skill], then we'll have to find the right medium between increasing variety but avoiding imbalance. There's probably some perfect amount of weapon variety.