IS THE DEFENSE STAT REDUNTANT?

I've never heard of a stat that increases resistance to the physical element. If you include both, then yeah, obviously that would be redundant. I don't know of any game that actually does that.

Games with complex relationships between statistics, like Tactics Ogre (PSP), the Star Ocean series, and the SaGa series, yeah, the Defense stat has a lot to offer in terms of potential.

In SMT games (at least the ones I've played) there is more than one physical element. So physical defense is no more redundant than magic defense.

author=Antilurker
they both do it nearly the exact same way (flat damage reduction),

Actually, it's not true.
In RM* default battle systems, for example, defense stat is a flat damage reduction while resistances are % damage reductions.

you're thinking of evade

author=LockeZ
I've never heard of a stat that increases resistance to the physical element. If you include both, then yeah, obviously that would be redundant. I don't know of any game that actually does that.

Besides SMT already mentioned, Ragnarok Online also does this with its DEF stat and item effects that have "-20% damage from Neutral element" ("Neutral" is more or less the element used by all physical attacks that don't have an inherent element). Slightly related is also Ragnarok Online's MDEF (magical defense) stat and item effects that have "-20% damage from <element>", which may or may not overlap depending on what kind of magical spell you're hit with.

My opinion is that DEF/MDEF is not a redundant stat, it covers things that <element> resistance stats may not. Oftentimes, I find that DEF/MDEF is the "general" defense guarding against most kinds of attacks, but not exhibiting any particularly strong effect, while <element> resistance is "specialized" defense which may or may not be super effective depending on the situation.

An example using the OP situation of DEF vs. Physical Resistance would be this:
A. Zack hits Ralph with a normal, no-element physical attack and Ralph has both DEF and Physical Resistance, thus damage is reduced by both counts.
B. Alex hits Arshes with a fire-element physical attack. Arshes has DEF and Physical Resistance, but Alex's attack which is of the fire element overrides the physical aspect and Arshes only gets to reduce Alex's attack with his DEF stat alone. The key thing here however is that Arshes still gets to use his overarching DEF stat.

Thus my opinion is that, given proper mechanics, having both DEF/MDEF and <element> resistance is not at all redundant. In fact, it brings into play another layer of strategy and tactics on both sides of the field.

I personally think it's totally cool to kill the DEF stat and just say something like "heavy armor gives you 50% phys resistance, light armor gives you +20% phys resistance/+15% evasion, and robes give you 30% magic resistance."

It's cool if doing so works in accordance to what you planned for the game. I don't approve of "just" doing so though.

I suppose you're right. Perhaps I'm to caught up with heavy planning with the numbers.

Physical Resistance is resistance to Physical attacks, but what exactly is a "Physical" attack? Is it melee damage? Is it ranged damage? Is it both? Is "Physical" an element? Is "Physical" any attack done with a physical object? The questions are endless.

Meanwhile, the DEF stat reduces damage from all (usually) non-magical attacks regardless of most secondary and tertiary characteristics. The brilliance of the DEF stat lies in its inherent vagueness and its independence from specialized resistances.