Other way around actually. During Vanilla, I mostly raided.
I didn’t do any significant PVP until very late in Vanilla.
I started raiding Molten Core with Leftovers on Silver Hand Server when Molten Core was the top raid instance available in the game. Leftovers was a server-wide organization with a unified loot DKP system. It had 7 or 8 full raid teams plus numerous pug teams.
After Molten Core I swapped to the number 3 guild on the server: Immortality. I did progression raiding with Immortality through BWL, ZG, AQ20 and into AQ40.
Unfortunately, Immortality got stuck on Twin Emps in AQ40. After 3 weeks of being stuck on that fight, the guild experienced the “Death Spiral”. It started with a couple top players being poached by the 2 higher guilds on the server.
But without those players progression was impossible (one was a main tank). We poached replacements from guilds lower down on the totem pole. But they weren’t geared. Unlike in Retail, back then the only place to get gear of sufficiently high ilevel for progression was farming the bosses we were able to down in AQ40. During this farming, more players got bored and quit, forcing us to recruit and gear more replacements.
It rapidly became obvious that Immortality’s place as a progression guild was done. I left the guild 2 months after we entered the Death Spiral. By then nearly the entire original raid team was gone. A new raid team was in place, but nowhere near the quality of the original one.
When I left Immortality, I joined Silence, which was the top guild on the server and at the time a Top 100 in the USA guild. As a member of Silence I full-cleared AQ40 and did progression in Naxx. I forget how many Naxx bosses we got down, but it something like 8 or 10. We eventually got stuck on 4 Horsemen.
Server transfers were out by this point and Silence itself decided to break up. Half the guild transferred from Silver Hand to Lightbringer and joined the top guild on Lightbringer: Eternal Reign (which itself was a top 100 guild for several expansions after Vanilla).
The other half of the guild stayed on Silver Hand and formed a new pvp guild: Fuzzy Wuzzy Bunny, which I joined. By this point we were only 3-4 months from the end of Vanilla. There was no way to progress in raiding without transferring off-server since none of the server’s remaining raiding guilds was capable of progressing in Naxx.
But we did have excellent players, with great teamwork, used to working on teamspeak, and with top-notch raid gear.
When it formed Fuzzy Wuzzy Bunny instantly became the top PVP guild on the server. 4 of its members became Grand Marshals and 4 became Field Marshals. I was one of the Field Marshals.
Prior to joining Fuzzy Wuzzy Bunny in the last months of Vanilla, I had only done sporadic PUG world and battlegrounds PVP. Nothing organized. The vast majority of my Vanilla gametime was spent PVE raiding.