This is true if it’s Rank 5 PvP. The Chaplain part of the build does not contribute anything to your PvP toolkit is what people are trying to say.
You can just as easily turn this around by going Cleric C2 - X - X - X - X/Oracle/Krivis - PD/Kabbalist.
Your Rank 6/7 normally define your “end-role”. Chaplain is normally taken at R5 for maximum effect (towards solo DPS and PvE).
This does not mean as Cleric with Chaplain in your build that you’ll be completely useless in PvP (this is just mind boggling unless it’s Rank 5 ONLY PvP). You just won’t be relying on the Chaplain (or even using it at all) part of your build during PvP.
Bonus: The Krivis at Rank 6 (w/c most “full support” builds take) can easily be replaced by an alt-char-Pardoner. You take 1 character slot (this is a downside to some), you gain “Team Exp/Level” and end up with a character that’s roughly around Lv126+ which you can easily push to Lv130 for additional “rush runs” for Talt/Trinity Sword/Petamion.
I have a Lv280 Cleric (with a Chaplain in it) which I built this way.
I purposefully chose Cleric 2 for C7 because I wanted to appear as “Cleric” when inspected and have Cleric as my main icon in parties. Other than that Oracle 1 is enough to cover basic Lv1 debuff prevention and ground magic elimination + magic damage prevention. Such is an example of how a single circle can fully change your character’s role.
This is true unless otherwise changed in the future (as with anything else in this game); change is the only inevitable thing. What this person really wanted to advise you is to not hope for any progression for hidden classes (Rank 2/3 onwards). However this does not mean you should never, under any circumstance, get Chaplain. He/she will not be playing your character and you can do w/e you want really.