Well it is kinda expected that it would this easy because of several reasons.
- Classic is based on the last patch released for vanilla, 1.12, so it is "complete" so to say.
- Consider that Molten Core was released in patch 1.1, BWL in 1.6, AQ in 1.9 and Naxx in 1.11
- With that in mind, the itemization and strength of classes where totally different in those patches when compared to 1.12
- Would have been interesting to see how popular Classic would have been if it had the natural vanilla patch cycle
- Vanilla/classic have had 15 years of theorycrafting behind it now.
- This was not the case during vanilla, everything was still new and being figured out.