Doesn't Availability refer to when in-game you catch it, not how hard it is to catch? Also, isn't it around a 1/7 chance of 1%!Bagon summoning Salamence?
I don't think we should tier Pokemon factoring in their encounter rate, because it's entirely possible to get a Salamence as it's first summon, no Adrenaline Orb even required. It should be mentioned in the Additional Notes or something how difficult something may be to encounter, but I don't think this should lower it on the tier list, Because then it's not in a spot that accurately reflects how it does in game.
Allow me to argue heartily against this. Well, attempt to anyway, I've had two nights with little sleep and I'm writing this while watching a movie. My language may not be the best right now.
We
HAVE to factor in the encounter rate when tiering Pokémon. Tiers are meant to reflect the performance of the Pokémon. How effortlessly they play through the game. Or rather, their relative lack of deficiencies, it boils down to the same. And availability can certainly be a big deficiency. Pokémon that are hard to come by are less reliable for an efficient/effortless playthrough. The hours you probably need to spend finding Salamence could be better spent, you know, progressing through the game.
The chance of a 1%-Bagon summoning Salamence is, to my knowledge, not 1/7, but 1/100. That means you have to go through an
expected value (look up that term) of 200 turns of battle before you find Salamence. 100 1-turn battles to find Bagon, 100 turns of Bagon battle before Salamence arrives. That is possibly the most grind-requiring Pokémon to find in any game, even worse than D/P Feebas. And grinding is antithetical to effiiency.
It is entirely possible to get Bagon as your first encounter, and Salamence as its first summon. The odds are roughly 1/10,000. Given that Sun and Moon have sold some 7 million units already, that should mean that more than 700 people have experienced this in their first play-through of the game. It is also entirely possible that Metronome will keep giving you 100+ BP moves every time you use it, or that Magnitude will strike 9 and 10 consistently. Or that Focus Blast will never fail you in crucial moments. But it's not something we can rely on. And that is the crux of the tiering. How much can we rely on this Pokémon to help you through the game, in every aspect of its being?
Salamence is unreliable. Period. Spend half a minute for every turn/encounter on average, and you may expect to spend three and a half hour finding it. You may find it sooner. Other people will find it later. But for the average player, across a large number of people, three and a half hour is the expected value. And that's not counting how easy it is to catch. That is detrimental to Salamence's reliability.
Overall, Salamence would perform very well if every player could be expected to find one with little effort. It is a very powerful and versatile Pokémon, after all. But the effort required to find Salamence is tremendous, which drags it far down the rankings.