Did you even Vanilla no ofc you didnt with a statement like this, you wont get passed Lucifron with 15 ppl not even in BiS Blues, do you really think half the raid was just standing around doing nothing?
Most classes were hell of alot easier to play back then and many had 1-3 buttons to even press to do optimal dps how shit do you think guilds were.
Garr you will need atleast 4 warlocks for example, good luck on baron when half your 15 man raid gets bombs.
And then there is Ragnaros which guilds wiped on for weeks after having all others on farm because of the dps needed to down him, your healers will be oom before the first set of sons are down let alone your 5th set with the low dps you will have.
Things may have been mechanically easy but most of those easy mechanics would literally kill you if you failed them.