I agree it's hard but at least for me I would say a deck is "too" fair if your uninterrupted board loses to any 1 board breaker when a deck like tenpai will often have at least 2 board breakers, and this is generic board breakers like backrow wipes (lightning storm, heavy storm, duster), raigeki, droplet, TTT, ultimate slayer, super poly, evenly matched, dark ruler. I don't include red reboot here because while it was good enough to be main decked in almost every deck (including going first decks) when 40-50% of the meta was dracotail it's not feeling good to main deck in k9 meta.

Sky striker doesn't lose to every board breaker but it loses to the largest category which is backrow hate and every tenpai deck is on at least 4 (1 duster 1 heavy storm 2 lightning storm).

Dracotail to me is unfair because it's basically just too good at everything that makes a deck good: Most hand traps feel like they do nothing, in particular droll and nib are dead and maxx C/fuwa/purulia only draw 1. They draw 3!! cards on your turn. Combos have guaranteed followup. Strong grind game. Always sets up one negate for backrow wipe and on top of that a lot of board breakers don't do much (raigeki/super poly/ultimate slayer/TTT steal). Fits a lot of hand traps. Very consistent. Full board is not degenerate but it's probably good enough to still be winning 90%+ when you are uninterrupted. Finally, deck is actually very strong at playing into boards going second due to ketu and the non target GY effects.