Brief RBY 1v1 tier list and meta thoughts
I got halfway through writing explanations for the A tiers before I realized I just don't care. I unabashedly think this meta is awful and combines the worst parts of both RBY and 1v1. Nothing below B tier is worth actually loading, since they're all ridiculous matchup fishes (Gengar, Sandslash), worse versions of higher tier mons (Zapdos, Articuno, Cloyster) one-time use lures (Persian), or Bad (Rhydon, Machamp). You could honestly ignore B tier too since the gap between them and the A tier in terms of matchup spread and reliability is so big. The 5 at the top are far and away better than everything else and it makes building stale and actually playing the game some kind of nightmarish 16-bit groundhog's day where you relive the same previews over and over. RBY's penchant for high variance does this tier no favors since unlike 6v6 there is no room to play around unfortunate luck, meaning that the absolute best, most concrete matchups are like 70/30 odds. This tier fails as 1v1 because of how few viable mons there are and how small their movepools are, leaving almost no room for any interesting lures. Just to squeeze any amount of novelty or surprise factor out you are forced to resort to things like Growl Persian, which beat one or maybe two mons and then force you to choose from three 1-2 matchups in game. The highest level of skill expression in RBY 1v1 is how well you can navigate the Snorlax/Alakazam/Jolteon preview. I would not recommend this tier be included in future editions of RBYOMPL.
I got halfway through writing explanations for the A tiers before I realized I just don't care. I unabashedly think this meta is awful and combines the worst parts of both RBY and 1v1. Nothing below B tier is worth actually loading, since they're all ridiculous matchup fishes (Gengar, Sandslash), worse versions of higher tier mons (Zapdos, Articuno, Cloyster) one-time use lures (Persian), or Bad (Rhydon, Machamp). You could honestly ignore B tier too since the gap between them and the A tier in terms of matchup spread and reliability is so big. The 5 at the top are far and away better than everything else and it makes building stale and actually playing the game some kind of nightmarish 16-bit groundhog's day where you relive the same previews over and over. RBY's penchant for high variance does this tier no favors since unlike 6v6 there is no room to play around unfortunate luck, meaning that the absolute best, most concrete matchups are like 70/30 odds. This tier fails as 1v1 because of how few viable mons there are and how small their movepools are, leaving almost no room for any interesting lures. Just to squeeze any amount of novelty or surprise factor out you are forced to resort to things like Growl Persian, which beat one or maybe two mons and then force you to choose from three 1-2 matchups in game. The highest level of skill expression in RBY 1v1 is how well you can navigate the Snorlax/Alakazam/Jolteon preview. I would not recommend this tier be included in future editions of RBYOMPL.