It was pointing out that perceived fallacy of your quote. OP cards are not justified if they only work on UP cards because it results in a forced combo. Furthermore OP cards that only work on UP card can still be OP.
But they are not OP at the first place, yes they can be OP if they are not limited to place on some cards.
Just like Adrenaline, if Adrenaline work with dragons as if it works with frogs they will be uber-OP, but they are not OP because they don't work with Dragons.
Limited to immortal offset the power of the card itself.
BTW, Slippery slope is not a proper way to "point out" a fallacy.
Perceived fallacious premise: OP cards are ok if they only affect UP cards
Attempted counter: If that is true then an OP card that buffs only Antlions is ok.
This is not slippery slope. It was attacking the perceived premise in its normal format.
1) Is SoW OP in the first place?*
2) If Immortals are UP and Wise Immortals are not UP then SoW is a forced combo with Immortals.
3) Notice that Frogs are not UP. They are irrelevant to the concern.
4) The proper way to point out a fallacy is to identify the perceived fallacious statement/premise, explain how the perceived fallacy would be relevant and then form a detailed logical counterargument. Neither of you fulfilled your duty to your assertion that a fallacy existed. However you misunderstood what he tried to say. So I clarified his position.
*
Here is my argument
so far SoW is the ONLY reason you use Immortals in a proper deck.
0) Immortal is UP and SoW + Immortal is not UP (see quote)
1) If Immortal is UP then a balanced Immortal would be stronger. (balanced > UP)
2) If a balanced Immortal would be stronger than Immortal then SoW + a balanced Immortal would be stronger than SoW + Immortal.
(SoW is a buff that only cares about immaterial)
3) If SoW + Immortal is not UP and SoW + balanced Immortal is stronger than SoW + Immortal then SoW + balanced Immortal is OP.
(Not UP = balanced or OP. Stronger than either is OP.)
4) If a card + a balanced card is OP then the first card is OP.
5) SoW is OP if Immortal is UP.