Dog piling on the wizard every encounter, however, isn't smart play; it's plain meta-gaming sadism. You dog pile on any one character, even the fighter, every encounter and I can guarantee that the guy will die sooner than later.
I didn't say dog piling on the wizard. That's your spin on what I said.
I said to avoid the heavily armored PCs for the lightly armored ones. Once the NPCs know that some PCs are being productive (healing, strong control, or high damage), then the focus of attacks should be on the productive PC(s).
And note: I also said semi-intelligent NPCs, not every encounter.
On the other hand, if one or two creatures decide to go after the wizard, the defender ought to be able to handle that. That's what things like CAGI, Threatening Rush, and numerous other defender powers are designed to do.
Interestingly enough, CAGI is 7th level. The PCs have to survive to get to that level (assuming the PCs start at level 1). Threatening Rush does mark multiple foes (at a lesser damage rate), but something that most DMs forget is that it's only the first NPC that might take damage when going off to attack other PCs. He shifts away, gets hit or not, and charges another lesser armored PC.
The rest of the marked NPCs can then shift away on their turns and charge different PCs, typically without retaliation from the Fighter. -2 mark, +1 charge, meh. An overall -1 to each attack is vastly preferable to attacking the high AC of the Fighter and at the same time, the Fighter typically hasn't done much more damage as if he had just attacked with a different At Will power.
Win win for the monsters.
Oh, the first NPC is bloodied? Then he delays instead so that a non-bloodied NPC can take the potential hit. Until a combat is nearing the end, this simple tactic works just fine most of the time. Course, the Fighter player doesn't have to use Combat Challenge on the first NPC that shifts away. Then again, there is no guarantee that saving CC will actually allow it to be used either.
Fighters are not nearly as sticky as many DMs make them out to be.
They force a creature to attack the defender by making it tactically inadvisable to do otherwise.
Actually, they don't. This control is mostly illusory and smart DMs know it. The designers thought that this is how it would work and it does work this way if the DM buys into the fallacy, but it's not actually true in fact if the DM plays his intelligent monsters intelligently.
Don't get me wrong, I recommend provoking fighter's marks. It makes combat more exciting for everyone involved. But the penalties also tend to make is so that the creature doesn't last long enough to take the squishies down.
This is pretty much false, especially for powers like Threatening Rush. The NPCs actually average a lot more damage by attacking lower AC PCs at -2 to hit or charging lower AC PCs at -1 to hit than they are having multiple NPCs wasting attacks against a Fighter's higher AC.
It's not like the wizard can't take a hit or two. According to you it's more like four and a half.
4.2 attacks, not 4.5 hits. It's 2 to 3 successful hits and 2 hits if the DM's damage dice are hot, and that's if the monster is same level with only one attack per round. Having multiple monsters or even one monster with multiple attacks can easily take out a first level Wizard in a single round.
At a 60% chance to hit, such a situation will take out a low level Wizard about 20% to 25% of the time.
I've seen it done quite a few times. Granted, Wizard players who do not follow your advice and take feats like Unarmored Agility have a greater chance of single round attack survival.
Healing can extend that further.
Yes it can. Course, healing Wizards wastes a lot of hit points in healing. Both because the Wizard was easier to hit and hence takes more damage overall for the group, and because the Wizard heals less, so the heal is less effective overall for the group.
Again, win win for the monsters (or alternatively, lose lose for the PCs).
One exception to this is when the party is low on healing surges, but the Wizard is not. Then it really doesn't matter if the healing is done on the Wizard (shy of the Comrade's Succor ritual). This can happen, but it's a bit more rare in campaigns where the DM has intelligent foes avoid targeting the heavily armored PCs.
Other party members, even non-defenders, can interject on his behalf, immobilizing his foes or penalizing their attacks.
Possibly. If the Wizard isn't already unconscious or under a serious effect already. By the time other PCs or even Defenders can come to his aid, even a single monster attacking can reek a lot of havoc on a Wizard.
Wizards also have a number of spells that allow them to push an enemy away or immobilize them. They have utility spells like shield and dimension door to manage spurts of attention. A wizard should be able to handle himself, he just can't tank the encounter. There's nothing wrong with that.
Yes, but again, the things you point out here are due to the fact that the Wizard is practically FORCED to take defensive feats and/or powers (some other classes are not), just to allow himself to manage spurts of attention. By definition.
A Wizard PC cannot really be designed like a Fighter or a Striker only for heavy duty offense (not necessarily damage, but even control), otherwise just a little bit of NPC attention can be fatal. The Wizard is more or less forced to put resources towards defense in some manner or other, or it's just a matter of time.
One can consider this a feat tax or a power tax or both. It's still something that the player of the Wizard is at least forced to contemplate because the power and versatility of the Wizard doesn't compensate for his frailty.
Also, regarding your example, a level + 3 encounter is intended to be hard! That's like complaining that the PCs had a hard time with a CR +4 encounter in 3e. If you don't like that level of challenge play encounters closer to your level and the problem is solved.
Did I complain once in that description? Nope. I merely was showing an example of the Defender not being able to protect the squishies. It happens a lot in 4E by challenging DMs, regardless of your claims to the contrary. Not just in harder encounters, but in similar level encounters with good monster placement/decisions and/or challenging terrain and other features.