Overall seems to be a pretty good list. You undervalue some of the champions based on their stand-alone presence rather than what they can do together as a team. Zilean/Rammus/Fiddlesticks/Kayle and Tryndamere are really annoying to deal with for example. You also pick out specific builds for champs and don't bother with others (AD Sion, AD Shaco, AP Teemo, AD TF, etc.). These are just my opinions based on my experiences (each to their own right?):
- AP Shaco, as has been mentioned before, is not Tier 2 at all - especially in Draft Mode of all places. AD Shaco has a much better start, early to mid game, but he kind of trails off late game especially if the other team is allowed to turtle.
- Akali. Since her nerfs, I wouldn't place her quite as high. Unless you're playing a ranged carry or a squishy mage with no CC, you shouldn't really have a problem with her. Not a very good pick in my opinion unless she's the last champ picked or used as a counterpick.
- Volibear is a very poor pick against any highly mobile champ, which most of the people in the tiers above him happen to be. I've had a Volibear on my team going against a Vayne, Morgana and Ezrael. Probably the most useless that bear has ever felt. That's just one example, but the counters to Volibear are also really easy to do. Should be dropped to Tier 4.
- Lux, while not as great a pick as Morgana, is still a good pick. She's very skillshot dependent and missing one can be disastrous, but let's be honest here, if you can't land your skillshots, why are you playing those types of champs? And if you're getting ganked, its not hard to fire your skillshot backwards and snare them, then throw down your slow in front of them. She's Tier 3 at least.
- Twitch isn't downright useless. He's just a poor pick. Tier 6 seems more appropriate. If you placed MF above Twitch, I think something is wrong there lol.
There are a couple of others that I disagree with that are based on more circumstances than anything else:
- Blitzcrank. I feel like you undervalued him a little bit. He's not great in all team compositions, but in some he works ridiculously well in.
- Soraka. Actually kind of surprised, she's that high. I must've missed the MO of where she was actually worth playing in a serious game rather than trolling the enemy team and laughing at their faces.
- Veigar. Since there's usually at least 1 AP champion on the enemy team, having Veigar present will send him home hurting. He's also pretty useful nuking down other AD Carries for your teammates as well. And by your description of the Tier he is in, I'd love to see a Karthus take on a Veigar any day when both are on the same level. Same for Xerath for that matter...
And Viktor, as much as I like him, should probably be Tier 5 or 6. The two spells that contribute the most to what is valued in 3s, dies with Viktor - making Viktor, a close up and personal mage, a big target. His slow/stun and ultimate both disappear whenever Viktor dies, and it's not that hard to kill him. On the other hand, I like using him against Tryndameres.
As a side note, everytime I see Pantheon and Xerath I usually jump for glee. It means I get fed regardless of who I'm playing (probably even Eve if I owned her). Could be I've yet to see a good player play them, but as far as I'm concerned, they're like Tier 6 to me. Too easy to kill and very little damage output unless fed, but then who doesn't?