It's fallacious to say that Razed Ruins is uniquely responsible for high katana damage. Weapon skills aside, it affects all melee weapons mostly equally. No weapon type is going to benefit from it moreso than any other in terms of sheer melee swings. In regards to weapon skills, it does help katana because Blade: Jin and Blade: Hi can crit, but crit weapon skills are not unique to katana.
Code:
Ascetic's Fury
Victory Smite
Evisceration
Vorpal Blade
Chant du Cygne
Rampage
Raging Rush
Ukko's Fury
Drakesbane
Blade: Jin
Blade: Hi
Hexa Strike
Jishnu's Radiance
All of those weapon skills and the weapon types that have access to them are thus enhanced by Razed Ruins in an almost equal way. The only exception to this is when the weapon skills can benefit from the 50 DEX through an increased WSC. Blade: Jin & Evisceration have a 30% DEX modifier while Jishnu's Radiance & Chant du Cygne have 60% DEX modifiers. Thus those weapon skills will receive either +12~13 or +25~26 to their WD from that 50 DEX. While nice, it's hardly exceptional, especially when contrasted to what other weapon skills may receive from cruor buffs. Blade: Jin vs Ascetic's Fury, for example.
Code:
Weaponskill STR VIT DEX
Ascetic's Fury 50% 50% 0
Blade: Jin 30% 0 30%
Assuming you're using Razed Ruins/Gnarled Horn/Apocalypse, then you're going to net +90/120 DEX, +40/70 STR & +40/70 VIT in various Abyssea zones. For Blade: Jin, this equates to WD +32~34 in Visions/Scars zones, WD +47-49 in Heroes zones. For Ascetic's Fury, it's WD +34 in Visions/Scars zones, WD +58-60 in Heroes zones.
I did leave a few things out. Classes that have critical attack bonus traits or gear will experience lower marginal gains from the +30% critical attack bonus on Razed Ruins. Ninja gets Kamome & Qirmiz Tathlum (also Loki's on Blade: Hi) for +15-20%, Monk has Impetus, which I'm not sure how to quantify, but I remember someone saying that it will average less than 15% and that's only while Impetus is up. Classes that experience enhanced critical hit rate through gear or abilities (Ninja with Innin, Monk with Impetus) will experience a lower marginal gain from the +30% critical hit rate on Razed Ruins.
Either way, saying that katana benefits Razed Ruins more than weapon class with a crit based weapon skill just isn't true. Hand-to-hand, for the most part, rides Abyssea buffs even moreso than katana.
Also, in regards to Berserk. Every weapon class benefits from this virtually equally unless you don't need it to cap your cRatio. Capped cRatio doesn't occur often without Berserk anyways. So, for the overwhelming majority of situations, Berserk is going to affect all weapon classes equally. The exception to this is when the weaponskill you're using doesn't use pDIF. There are a few of them, such as Wildfire, that behave this way, but those are niche cases. So implying that Berserk is somehow less considerable because of Razed Ruins or katanas or whatever is also fallacious.