By and large, I have found that most competent mage players are far more apt to give consideration to the entire party, who has what skill loaded, etc., than warriors or rangers, who tend to focus solely on the power of their own swords and bows under the maxim that each should hold his own ground. While it's true that each person should be capable of standing on their own two feet, and that doing so is probably better EXP for everyone involved if they would just go solo, party play has an entirely different mechanic, one which competent mages tend to more naturally embrace due to its strategic nature.
IMO, it takes far less strategy to play a mage. With melee, you have no spammable skills unless you have your target up against a wall. In higher level dungeons, your ability to OHKO with smash or windmill is taken away from you. Massive multi-aggro is thrown in your face. At the end of every attack sequence you make, you are wide open to attacks from every direction, both melee and ranged.
On the other hand, a mage can easily spam his high cost skills to no end. Stunlock is easily possible with bolts, Thunder, and Ice Spear. OHKO can still be done with a critical advanced magic spell - the only drawback is the preparation time. But wait, you can load your skill before opening the chest or hitting the orb, eliminating that drawback for the first wave. Multi-aggro isn't a big deal, you can erect walls or send pets to their doom, while you're sheltered safely in your corner. There's no post-attack recovery phase like melee, you can just lock and load continuously with no down time.
As for the who-should-be-supporting-whom bit, it is very, very true that mages should be the ones being supported, not the other way around. I've lost count of the number of careless warriors who simply Windmill every tightly-packed mob without a second thought to the long preparation and large quantity of MP put into my fully-charged advanced spells. Keep the mage alive, and he will keep you all alive. If you're going to party with a mage, stop playing Rambo and start thinking strategically, like the mage already is.
It seems like your entire argument is based on the fact that warriors are brainless idiots who just attack, attack, attack regardless of his/her surroundings. If that's the impression you get, then you're obviously playing with some terrible people. I've done runs with people who are smart enough to rush into battle without dispersing mobs so that they're still vulnerable to my nuke. It's entirely possible for a melee player to dish out a decent amount of damage without disrupting a mage's efficiency, and it's crazy to say that warriors should halt their potential 1,000+dmg/0.8sec windmills to act as a bodyguard while a mage loads a potential ~8,000dmg/~14sec spells.
As Rime said, all characters should be supporting each other to attain the best possible DPS. Since everybody has a unique playstyle, this is more common in repeat parties, such as friends or guilds. If everybody prefer to solo all the time, then that explains why your party lacks synergy and your party dynamics are rotten.