(Psi)SeveredHead
Adventurer
I would begin by questioning the assumption that I've bolded. I was going to say more, but what I'd written read like a massive anti-4e-rant, so I decided to withold it. However, given the open-ended nature of ritual magic (and especially the "fly, teleport, and turn people into frogs" applications), and also given that (I think) Wizards have received more splat-material expansions than any other class, I would be inclined to question whether the classes are actually balanced.
The role system makes it very difficult to compare classes filling different roles. When people talk about 4e balance, they're usually talking about which class fills that role better. Most fighters (other than slayers) are defenders, and most wizards are controllers. They simply don't fill the same role.
Slayers and blasty wizards are essentially strikers (blasty wizards are technically controllers, but only technically) but even then, slayers are good at single-target damage and blasty wizards are good at roasting multiple targets.
They're considered balanced because their rules aren't too different, and (not that PvP is designed for balance) neither have "overwhelming" abilities that could completely shut down the other side.
Rituals aren't a huge balance concern between classes. Most rituals are a party resource rather than something used by and for only the ritualist PC; many actually give benefits to all the participants. (An example might be Traveler's Camouflage. This lets a group make a really good Stealth check, but of course all the participants have to "dance" for the casting time until it's ready. Also, once combat starts the ritual ends, so you don't have enemies guessing which square everyone is in. It's great for surveillance or setting an ambush though. This sort of ritual is basically a significant party buff.) I've seen very few rituals that would worry me as a DM.
The ability to Fly as a ritual (Overland Flight, a 20th-level ritual) is quite weak. The ritual actually ends if the wizard starts fighting, and you don't move so fast that enemies with ranged attacks can't try to stop you. Here are my short-form notes on the ritual: "The ritualist and allies within 5 squares gain overland flight 20. All minor, immediate and standard actions are lost, and move actions can only be used to fly. The flier flies 20 squares as a move action. Doing anything else causes the flyer to crash. With typical rests, the fliers can fly 100 miles." A far cry from "fly at speed 50 or so for hours at 9th-level, no restrictions beyond Dispel Magic." If I were seriously worried about this ritual, I've give it an altitude limit, but that's it.
The ability to Teleport is under the DM's control. When a wizard learns the ritual, they learn the sigils for two teleportation circles. That's it. Teleportation circles are usually found in mage guilds, temples, etc, not just any random place. Anyone popping into such a place could easily face an encounter, including traps, and said encounter could be out of their league. What won't happen is teleporting into the main villain's bedroom, buffed to the gills (long-term buffs are pretty much non-existent for combat purposes) and ganking him immediately. Even True Portal, the 28th-level version that can teleport you into the villain's bedroom has restrictions and can be blocked by the 20th-level Forbiddance ritual.
There's no ritual that I've sen that can turn someone into a frog, but if there is, then like the Imprisonment ritual it would have a casting time of 5 minutes, and the target must remain within range for that period, without ganking you for those 50 rounds. In short, you have to defeat an opponent first before you can turn them into a frog. It's not combat, it's punishment. Witches can turn allies into frogs, and there's a few NPC wizards that can do something similar, but first they must "hex" the target, and the target is only turned into a frog until they save.