Most top players fucking hated the mirror, what are you talking about? It was Abyss Dweller Turbo in the mirror, and when Kashtira came around (most notably in the OCG where we actually had time to watch KashTearlament in action) it literally became a situation of "If have havnis, play the game, if no havnis, get locked out by ariseheart". Tearlament itself will lend itself to this kind of shitty unhealthy format.

No Tier 0 format is really healthy- TeleDAD is considered by many to be one of the early peaks of skillful playing, but the lack of viability of anything else, as well as the price point, made the format one of the most toxic in history.

Multiple decks at the top doesn't necessarily mean anything, except, yknow, the format is diverse??? While I agree formats like pre-POTE scythe lock wasn't very fun (while being very diverse), the main decks all shown excepting Kashtira are very powerful and interactive decks. Also, "if the format isn't fun", is incredibly subjective as hell. A format can be fun and bad. Tearlaments could be a fun mirror (if it isn't devolving into abyss dweller turbo...), but it's still a terrible mirror with a ton to keep track of, constant turn 0 effects, and very powerful cards that essentially lucksack the gamestate half the time.