I already debunked that nonsense via Inn. A hypothetical Inn without the on-gain effect that costs 5$ is strictly worse than the real Inn.
So your rule which says that on-gain and on-buy effect are irrelevant is obvious nonsense.
No, you did not. A hypothetical Inn without the on-gain effect that costs $5 is not detrimental to the game because it's strictly worse than the real Inn, it's just a pretty boring and weak card in a vacuum. It also doesn't address the facts that:
1) In games where only one of the cards is present, it doesn't matter if Village is strictly worse than Secluded Township
2) In games where both of the cards are present, for $3, players can choose to gain a card which just says +1 card, +2 actions, or a card which says +1 card, +2 actions and makes you gain a curse and topdeck itself on-buy. This remains true regardless of if Secluded Township can also act as a regular Village or not.
"On-gain and on-buy effect are irrelevant" is not a rule. It is the lack thereof. "Cards being strictly better than other cards is relevant" is a rule.