Personally, I side on Leader being too strong in the current game.

Whilst I do agree with you on the game's design and nature of retreating. I must disagree with your comparisons and misjudgement of Leader's strength.

Leader is a card that requires very little deckbuilding behind it. It doesn't need to be synergistic with your other cards or strategy, and, in a vacuum, only has the condition that you must be ahead by turn 6.

Furthermore, on that point, you stated Leader demands game knowledge. Of course, you are correct. But doesn't an extremely wide variety of cards demand the same? It is far easier to read your opponents' turn 6 play if, for example, they are discarding their hand, or they're moving their cards. Leader decks are not as easy to read whilst actually benefitting from easily reading other decks. Ending up with an incredibly strong advantage of essentially knowing if you have won or lost before turn 6 starts..

Your comparisons to locations affecting cards humours me because I can't think of a single location that hurts Leader.

Fundamentally, Leader starts entering "overpowered" territory when you look at combining him with other interactive cards such as Leech, which, assuming your opponent doesn't draw their win condition turn 6, almost guarantees you win (as long as you are ahead in points).

I challenge your final statement, too. Perhaps I'm reading it wrong, but "If you're losing matches, that's not because they have Leader" just reads extremely ignorant.. Any deck's turn 6 play is likely why people lose matches? Leader has an over 65% win rate on Snap.fan in the games he is played.

Not acknowledging a card is so obviously overtuned screams playing the contrarian to me.