The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul). The guides have been tweaked many times over the years to make things "faster". The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms. I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
Our initial runs exposed a few (expected) issues: the game sometimes crashed, didn’t recognize our modern video cards, and was incompatible with our current login system. That first pass also couldn’t support any of our modern security and anti-cheating capabilities. Clearly we had a lot of work to do to make WoW Classic live up to the Blizzard standard of quality, and deliver the experience players want.
For another example of lighting, we looked at Elwynn Forest. We had a period in Warcraft’s history where we changed all the lighting equations and as a result, our environment artists had to take a pass over all of the zones to improve the lighting and take advantage of the new equations. To recreate the original experience, we had to rewind those changes. The first thing we did was restore the old lighting data. This brought us much closer to the original lighting—and with a few more changes to the distance formula, fog formulas, and some changes to shadows, we were able to bring things even closer to the original lighting.