Conceal Spell - rank limitation on static DC

[MordredofFairy]

Conceal Spell wrote:

You can hide the evidence of spells you cast.

Prerequisite(s): Deceitful, Bluff 1 rank, Disguise 1 rank, Sleight of Hand 1 rank.

Benefit(s): When you cast a spell or use a spell-like ability, you can attempt to conceal verbal and somatic components among other speech and gestures, and to conceal the manifestation of casting the spell, so others don’t realize you’re casting a spell or using a spell-like ability until it is too late. The attempt to hide the spell slows your casting slightly, such that spells that normally take a standard action to cast now take a full-round action, and spells that normally take longer than a standard action take twice as long. (Swift action spells still take a swift action.) To discover your ruse, a creature must succeed at a Perception, Sense Motive, or Spellcraft check (the creature receives an automatic check with whichever of those skills has the highest bonus) against a DC equal to 15 + your number of ranks in Bluff or Disguise (whichever is higher) + your Charisma modifier; the creature gains a bonus on its check equal to the level of the spell or spell-like ability you are concealing.

If your spell has a somatic component, any creature that can see you receives a Perception or Spellcraft check (whichever has the highest bonus) against a DC equal to 15 + your number of ranks in Sleight of Hand + your Dexterity modifier; the creature gains a bonus on its check equal to the level of the spell or spell-like ability you are concealing.

Since you are concealing the spell’s manifestation through other actions, others observing you realize you’re doing something, even if they don’t realize you’re casting a spell. If there is a verbal component, they still hear your loud, clear voice but don’t notice the spell woven within.

If an opponent fails its check, your casting also does not provoke attacks of opportunity, and an opponent that fails its check can’t use readied actions that depend on realizing that you’re casting a spell or using a spell-like ability, or readied actions such as counterspelling that require identifying the spell you’re casting. Spells such as fireball that create an additional obvious effect (aside from the manifestation of casting that all spells and spell-like abilities share) still create that effect, though it might not be obvious who cast the spell unless it emanates from you.

If a character interacts with you long enough to attempt a Sense Motive check without realizing you have been casting spells, that character can use Sense Motive to gain a hunch that you’re behaving unusually.

Emphasis mine. The Feat has Deceitful as a prerequisite, but as written, the DC for both checks is 15+ranks+governing attribute.

Since it specifically calls out ranks, that means no other boni get into play.
For comparison:

Feint in Combat wrote:

You can also use Bluff to feint in combat, causing your opponent to be denied his Dexterity bonus to his AC against your next attack. The DC of this check is equal to 10 + your opponent’s base attack bonus + your opponent’s Wisdom modifier. If your opponent is trained in Sense Motive, the DC is instead equal to 10 + your opponent’s Sense Motive bonus, if higher. For more information on feinting in combat, see Combat.

In Feinting, for example, the full Sense Motive Bonus is used to set the DC.

But for Conceal spell, you actually only count the ranks plus attribute. That means no class skill, no deceitful bonus...also no racial, trait, insight, competence, luck, insight, unnamed etc... bonus.

Considering the Feat already requires you to pay a follow-up Feat Tax to remove the scaling penalty on spell-levels, and usually will allow 2 opposed checks, it seems very harsh to basically shoot the caster in the knee by artificially limiting the DC he can achieve.
The prerequisite of Deceitful not helping in any way also feels weird, as does that a charismatic sorcerer with ranks in sleight of hand does better than a wizard with the same number of ranks, who made it a class skill, got skill focus for it, and wears a circlet of persuasion.

Was this worded in an unfortunate way, or is this really the intent?

[Plausible Pseudonym]

We debated this when it was released. They apparently don't like hiding spellcasting but felt they needed a core, PFS allowed option in an intrigue book.

Cunning Caster is a better option for many, especially psychic casters.

[Koi Eokei]

As a DM, if my player wanted to pick up this feat, to essentially do what it's supposed to, I'd let him add all of his bonuses. 3.5 had similar rule systems:

Races of Stone has a section in skills, which outlines how you can use Slight of Hand to conceal spellcasting. There is no special requirement:

When casting a spell, you may make a Sleight of Hand check to make your verbal and somatic compo- nents less obtrusive, muttering magic words under your breath and making magic gestures within your sleeves. Your Sleight of Hand check is opposed by any observer’s Spot check. The observer’s success doesn’t prevent you from casting the spell, just from doing it unnoticed.

Action: None. You make the check as part of your normal spellcasting

Complete Scoundrel has a skill trick called "Conceal Spellcasting" which also lets you make a slight of hand check vs. an opposed spot check to conceal spellcasting:

You can cast a spell without revealing that you are doing so . Make a Sleight of Hand check as part of the action used to cast the spell, opposed by the Spot checks of onlookers . If you are successful, an observer can’t tell that you’re casting a spell . That observer cannot make an attack of opportunity against you for casting, nor can it attempt to counter your spell.

The wording on the two abilities are relatively similar. "Conceal Spellcasting" has a bit more about counterspelling, where Race of Stone's skill section focuses more on whether they realize you're casting.

The fact that it calls out ranks, makes not a lick of sense to me. Here's the difference
Class skill +3
Trait +1
Skill Focus +2
Circlet +3
Tap inner beauty +2
Total +11

Some crappy wording and you miss out on being able to add 11 to the DC!! And that's without even trying. Let alone the investment for the Dex side of things.