[Sawrock]

Ogata's Waraji (+2 CEL, +10% Physical Damage Reduction) only works when wearing unarmored armor.
Black Knight's Indomitable (+10% Physical Damage Reduction, doubles if Black Wind is used and if Black Knight is your main class) only works when wearing heavy armor.
In my opinion, this makes Ogata clearly more useful- you can be dodgy, and get tankiness as well. While Intomitable is situationally more useful, it's just that- situational, and otherwise the same bonus. It also, mind, doesn't provide the +2 CEL boost that Ogata does, and while that may seem a small stat boost, it it still an advantage none-the-less.
These are some suggestions that could be used to fix the situation, in my opinion:

1. Changing how Indomitable works
Make Indomitable start with 10% damage reduction, add 10% if you used the Black Wind (without requiring Black Knight to be your main class), and then, if Black Knight is your main class, add 10% more damage reduction as well. This leads to the following scenarios:
10%: Heavy Armor, BK Subclass, No Black Wind
20%: Heavy Armor, BK Subclass, Black Wind
20%: Heavy Armor, BK Mainclass, No Black Wind
30%: Heavy Armor, BK Mainclass, Black Wind

2. Changing how Ogata works
Make the physical damage reduction on Ogata work like Evasion from Rogue: it works only on autohits if you would pass an evade check to reduce the damage.

[Rendar]

Ogata only works if scaled CEL > Scaled Def. (or if Kensei main; always)

Indominatble works always.

Black knights are not exactly meant to be SUPER FAST.

If anything, I'd like to see a decent number of the BK passives/innates changed to just be 3 rank skills.. because it's nigh impossibly to choose anything if you go take the innates/passives that all fucking work on eachother.

[Autumn]

I think Indomitable itself should be buffed in some way, that'd be nice, strictly its worse than other 10% DRs cause its has a heavy armor requirement, heavy armor itself has downsides such as reduced evade, movement and not being eligable for some skills such as wraithguard, kip up and evasion.

Its no wonder why some people would rather go ogatas + WB or 1v1, strictly its just better than anything Indomitable will offer for the downside of heavy armor.

[Neus]

I don't think they're really comparable. Ogata requires a leg slot, Indomitable doesn't.

[Autumn]

Indomitable requires a torso slot with a vastly inferior armor type, not to sound rude but one or the other needs a buff at some point, I once suggested armor talents that'd probably help in some way.

Most people need STR for B/W so they can even equip heavy armor most of the time, I think Saw raises a good point however, not a lot of people consider indomitable over ogatas ever, they'll either equip other DRs like weathered body or wraithguard, use Kensei and equip ogatas, I talk to a lot of people over their builds too much to know this.

I think in the end of this post, I should just mention that high armor values mean little in these days where percent based damage reduction is king, and how good unarmored is compared to heavy armor most of the time (Looking at armor of eyes and cloak of many colors specifically)

[Chaos]

I don't think they're really comparable. Ogata requires a leg slot, Indomitable doesn't.

Indomitable requires a torso slot and a class slot. I'd call that more important than a leg slot.

I'm gonna have to agree with the OP: Either a buff to Indomitable is in order, or Ogata needs an adjustment to get it off the same page as Indomitable.

[Rendar]

Actually, I'm gonna be changing my mind on this.

Ogata is a little overbearing. However, it's overbearing only because it has the "If Kensei main; ignore CEL > DEF"

Which means you can just build a fat kensei and hunker down with tons of additional DR. I'd like to see the Kensei Main bit removed, or the item get reworked in some fashion. I run it on my Kensei/ST. Namely as a necessity since evasion got hit with the nerf bat a few dozen times.

[Autumn]

I think the Kensei main class thing is rather creative and a good thing, for Kensei vs Ghost argument especially.

[Neus]

Indomitable requires a torso slot and a class slot. I'd call that more important than a leg slot.

Debatable.

[Chaos]

I don't think it's debatable. Unarmored fits with so many skills and possesses so many good selections that it's not even a drawback for a Legs item that grants Physical DR. Heavy Armor gets one skill and then proceeds to cancel out at least three other (solid) skills, and has a more limited selection for anyone that isn't a Dullahan. Stack that on how neglible Heavy Armor's main stat (see: Armor Defense) is, and a Heavy Armor requirement becomes a drawback.

Armor imbalance aside, at the least, you're looking at Ogatas performing on-par with Indomitable without being limited to only bulk-toting Black Knights. This applies doubly for evasive builds. I do not see why evasive builds should be getting the same level of passive, slap-on-and-forget physical DR that a tank class should get.