Also what's wrong with wanting to run all raids as a caster? You can run all raids as melee dps and ranged too, so....
This is my problem. I have several martial characters ready for raiding. And I like to play them. But I want to play them just as easily with my other caster characters. What's wrong with being able to play raids just as often on my uber-completionist wizard as on my weapon-user characters (who have a fair amount of work behind them in the build, but not as much as my main character)?
Because knowing DDO's mechanics, the experience of the Raid, and knowledge of your own characters limitations, doesn't make you more skilled than others at performing well in DDO?
Also, the example was given in that there can be players out there, more than capable of solo'ing the run for the 11 other pikers, but if they pop up on a class (like a Wizard) that others are shunning, then it reaffirms the issue OP was describing.
But yes, I will agree, that it also highlights that the core caster issues that are brought up often by some forum goers (including yourself) on that casters are in a bad situation, does look bad when compared to mine and what I can do on a caster (Wizard of all classes, which is often touted as the worst).
Whether it was play/gearing/build, it doesn't matter. Do you know why? Because all of my test toon builds use common things in DDO to prevent myself from ever being nerfed by the Devs.
There are several things I'd like to clarify here. First, I agree with you that people greatly underestimate what a wizard can do. And I know this because with a wizard I do things that others say are impossible. In general, I find that the builds people do nowadays are bad for wizards. Many players gimp themselves by following the DDO wizard build tradition, which has imposed certain ideas on the class's builds that aren't beneficial to their performance.
And this could apply, although to a lesser extent, to other casters. So, well, you can say that part of the problem lies with the players.
Now, you can't say: there isn't a problem with casters and raids.
There's no doubt that raids are designed for weapons. The moment the only challenge is sustained DPS, magic is at a disadvantage. The moment there are a million immunities to magic but not to weapons, you know who's at a disadvantage. We also can't forget that developers are obsessed with bosses and barely give room to CC or IKs in raids; that's a tertiary or almost non-existent role in modern raids. And why are all bosses immune to CC and not damage? Where are the damage-immune bosses that NEED be controlled?
Second, there's a problem with caster DPS. It's not as big as some say, but it's undeniable that in burst and sustained DPS, casters are behind. You say, there are several ToN solo completions with a wizard, you're exaggerating. It's true, a wizard can solo that raid. But what were those completion times compared to weapon users solos? Wizard completions took much longer than weapon user ones. Mind you: I'm not taking any credit away from those wizard completions. It's not easy to just solo a raid. But times are what they are, and they are what they are because caster DPS is way behind of weapons.
Look, when top-ten players who loved casters have thrown in the towel and are now martial toons, it's for a reason. If it were just a matter of build, there would be top-ten players playing casters.
Third, because most people don't do a great job with caster builds, and very few uber players play casters, what you're going to get with a pug is a majority of bad casters, which will weigh down the raid and make leaders hesitant to pick casters.
Don't tell me that a well-built caster can do much more than many of those leaders who reject casters believe. I know. I know because my casters can do it. I know that a caster can be very useful on low difficulty in a raid. I know. From experience. But many casters on pugs aren't going to be that useful. And on a pug, a poorly built/geared martial generally does more than a poorly built/geared caster.
And then we have the last thing. Look, I know that casters are more useful than some people think. But we can't fool ourselves. Our DPS is gimped compared to what a well-built martial can offer. It's reality. We can't turn a blind eye to it. Yes, next to a bad martial toons, a good caster may look good. But with a well-constructed martial build, they'll be left behind. That's the way it is.