The main issues with RBYK210 were that its founders were assholes who were more interested in trolling and belittling others--especially older players--and how esoteric their circle really was. Only a handful of people experimented with their tiers (tiers which were, to a large extent, not tested in tour play), all of whom would stop playing a year or two after the site was established. Activity in tours was also a major problem, as about half were canceled in its first year. And let's not forget the anniversary tour, which took half a year to reach the finals despite the cash prize and was actually canceled--in the finals.
I will say that one significant development they contributed to the metagame was Gengar's influence. Gengar became a lot more common from 2010 up until about 2013, which was when I introduced FriendlyMie on the PO ladder. Gengar usage gradually began to plummet over the next couple of years.
Going back to the topic of tiers, we did have tiers on GameFAQs in 2003, but they were, as Hipmonlee said, largely determined by gut feelings. For example, in the summer UU tournament my opponent used Persian, which is considered OU now. I used Victreebel in the semi finals and Cloyster in the finals, which are obviously OU Pokemon by today's standards. There was, however, a tier on GameFAQs called "restricted UU," which was basically the ancestor to NU. I wrote up a tier list for it based on Haste2's recommendation, though in retrospect it was pretty inconsistent. For example, the tier had Butterfree, Magneton, and then Charizard, who is obviously a step or two above the other two.
In 2004 an attempt to write an official tier list on GameFAQs was attempted, but the thread was derailed by trolling, inability to compromise, and also not enough people contributing (it was largely just me, Redwall Dude, and maybe Hipmonlee). When I created THE Alternative in 2005, a major goal of mine was to create an official tier list. I divided my tiers into OU, BL, "top UU," "UU," and "NU" (NU was originally "restricted UU"), and finished the project in 2006. I made a few changes here and there over the next two years, ending up with these tiers in 2008.
OU
Tauros
Alakazam
Chansey
Exeggutor
Slowbro
Jynx
Rhydon
Golem
Zapdos
Articuno
Starmie
Snorlax
Lapras
Gengar
BL
Persian
Raichu
Jolteon
Hypno
Clefable
Kangaskhan
Moltres
Dragonite
Golduck
Gyarados
Mr. Mime
Top UU
Tentacruel
Electabuzz
Dodrio
Machamp
Sandslash
Charizard
Nidoking
Venusaur
Victreebel
Dugtrio
Blastoise
Cloyster
Omastar
Kabutops
Tangela
Nidoqueen
Weezing
Poliwrath
Kingler
Pinsir
Raticate
Fearow
Vaporeon
Ninetales
UU
Wigglytuff
Aerodactyl
Hitmonlee
Venomoth
Onix
Muk
Scyther
Marowak
Pidgeot
Lickitung
Porygon
Vileplume
Arbok
Rapidash
Primeape
Electrode
Magneton
Magmar
Dewgong
NU
Ditto
Farfetch'd
Hitmonchan
Golbat
Butterfree
Beedrill
Parasect
Seaking
Seadra
These tier lists would be used in the German circuit, primarily on Pokemonexperte and Pokefans, and were definitely referred to by the RBY2K10 people. However, like with RBY2K10, these tiers could be scrutinized for a dearth of contributors (though there were twice as many finished tours on TA than RBY2K10, so the sample size was much larger, at least).