Patch Available - KMST 1.2.406

Nope.
Mercedes has ridiculous amounts of damage reduction and evade skills, totaling up to like 60% evasion and 50% damage reduction or some ridiculous as f'uck number. Taking 0 damage > taking 800 damage.

Evading isn't tanking, but Paladins do plenty of evading as well.
I'm curious what those skills you speak of are.
"or some ridiculous as f'uck number" indicates to me that you aren't actually sure yourself.

EDIT:
Checking through the skill tables for Mercedes, I found these:
Potential Power - Active Effect: MP Cost: 60, Duration: 180 sec, Weapon Attack +40, Passive Effect: Evasion Rate: +20%
Water Shield - MP Cost: 100, Duration: 180 sec, Damage Absorbed: 30%, Status Effect and Element Resistance: +25%
Ancient Spirit - Active Effect: MP Cost: 80, Duration: 210 sec, Damage: +30%, Passive Effect: Ignis Lore's Evasion Rate +20%

Total: 40% Evasion Rate and 30% Damage Absorb.

As high as those are for a ranged class, Paladins do both better.
I'm not a big fan of hyperbole when it comes to solid numbers.

Blast is awful in a sense that it's only marginally better (in perfect 1 vs. 1 scenarios) than Advanced Charge Blow (which hits 7 mobs and stuns) and it has the shortest range of any 4th job skill in the game.

Stance in 2nd job would free up 3rd and 4th job for better skills.

Well, Blast needs better range for sure as well as an animation that doesn't shrivel when compared to CB.
However, it's actually quite a bit better than ACB in a 1v1 scenario if you actually bother to pay attention to all of its special properties.

There's no reason to have Stance come so early. Yes, it should be out of 4th Job, but it can fit in perfectly in 3rd.