I will agree with the 2nd part and while the first part has truth to it, you have to consider the argument I am presenting in that while Taskmaster clearly has very good stuff... the top 5 just has better. Since you listed his good stuff, I am going to list some good stuff of the top 5 for comparison sakes.
PHOENIX
Not even going to bother listing her good stuff. It never ends.
WOLVERINE
*The most imperceptible mix ups in the game. God's Beard said it the best "invisible 4 way mix up".
*Invincible special that covers at least 3/4th of the screen
*King of decimating characters upon incoming after deaths or snap back
*Highest kill ratio in the game, highest happy birthday rate as well
*Super easy and good damaging BnB. Has a combo that can kill with 2 meters and it's easier than Taskmaster's.
*Very little scaling on his moves mean he kills so fast in X factor that he has enough time to kill another character on in-coming.
*Godlike throw game as every touch leads to death if he wishes. One of the few characters in the game who can kill off of a ground throw.
*DIVE KICK... enough said
*Brain dead f+H, Drill Claw, Dive Kick, air throw option selection game
*Fast dashes, fast and high priority normals. One of the best Ls in the game. Standing one is fast, crouching one shrinks his hit box and has great range plus can be rapid fired and hit confirmed into a combo after like 5 presses. Jumping L is an INSTANT OVER HEAD.
*Very small hit box when crouching, even gets under Tron
*Berserker Charge makes a very dominant character into a god. Loops everywhere, makes everything safe and allows him to hit confirm with B Slash into a full combo.
DANTE
*One of the best if not the best range/hit boxes on normals
*Some of the highest damaging, highest meter building combos in the game
*Gets insane damage off of a hard knockdown (like Haggar assist) or possibly even a kill. Haggar + Dante is at least as good as Wolverine + Akuma.
*Has the best move in the game: Hammer. Complete invincible, hits overhead, great hit box, +20 on block and leads to TOD combos. And guess what? It beats the DIVE KICK
*Excellent IAD game and combined with his hit boxes allows for some of the dirtiest cross ups/unblockable game in MVC3
*A safe, 3/4th screen poke that can be used to hit confirmed into a combo
*Can make any of his normals safe using Bold cancels and can get out of situations most other characters can't thanks to this mechanic
*Only character who has access to a mini-X Factor that gives him 2 of the best moves in the game. A super fast, high damaging and high chipping full screen beam and an invulnerable dash attack that leads into TOD combos.
*Has a TRACKING TELEPORT
*For a character built around rushdown and combos, Dante's zoning game is one of the best in the game thanks to his high ranged attacks and good number of projectiles (some of them are homing)
*Dirty mix ups on in-coming characters using Acid Rain
*2 great assists, Jam Session is one of the best assists in the game due to how much utility it has
*Can both start and end the DHC glitch. One of the biggest abusers of the glitch in the game
MAGNETO
*Fastest beam in the game. So much of the cast can't do shit about the Disruptor it's one of the most dominant projectiles in the game. Also available as an assist.
*High damaging and high meter building combos
*GODLIKE air throw/ground throw game which almost always lead to character death. Doesn't even need an assist to combo off of it.
*J.H is one of the most dominant normals in the game. Crosses up, huge range, great hit stun, OS with air throw, leads into air loops and TODs.
*The fastest tri-jump in the game. If you are standing on the ground and blocking low... you have just been opened up by Magneto.
*One of the best rushdown in the game COMBINED with one of the best runaway/zoning game. Makes so many other characters obsolete.
*One of the best if not the best LVL3 in the game. Full screen, easy to combo into and can be comboed after.
*One of the few characters who has an even match up against Dark Phoenix.
*A major abuser of the DHC glitch because of his ability to start it after his Hyper Grav loop.
WESKER
*One of the best characters in the game who doesn't need meter to wreck a team. Top of the list for point character in a Phoenix team.
*Superb reset/mix up game, in the corner you are pretty much put into a vortex of mix ups
*After Phoenix, the most absurd X factor bonuses in the game. 200% damage boost with a speed boost on an already very dominant character
*Low gun shot assist gives your team access to relaunch combos and unblockable set ups. One of the best assists in the game
*Dominant normals that are generally safe on block and have high priority
*One of the best air throws in the game which can be reset back into. Can do this all solo
*Deadly Command throw game (1 frame command throw leads into high damaging combos)
*Gun shots are a great zoning tool and if used as an anti-air lead into full combos. Also gun shot loop in X factor
*Combined with assists, Wesker has some of the dirtiest cross ups in the game thanks to his teleport shenanigans
*Counter hyper leads into a full combo (as compared to Taskmaster's which doesn't)
*Out of the top 5 he has the highest health which leads into situations where he edges out a win with just enough life remaining due to the meter he has built over