While the expansion kicks off with heavy references and scenes of this war, leveling through the Horde side of the new content it barely came up again. Except for all the times I had to mine Azerite to make sure my faction was the leader in the Azeroth version of a nuclear arms race. The Alliance side of things had some heavier references to to the war, at least in the portions I played, with one scenario in Stormsong Valley where a fleet of Horde aggressors bombed a town.
5% was admittedly an exaggeration, just felt that low. I'd say it was probably closer to the 30-40% range. It was Artifacts of the Blacksilt, spent a good 10-15 minutes killing Blacksilt Seers to get two damn idols to drop. A quest that had me killing Elder Brown Bears for bear flanks also took quite a while, though that was less due to drop rate and more due to how spread out they were.
Aegwynn - Alliance Aegwynn - Horde Aerie Peak - Alliance Aerie Peak - Horde Agamaggan - Alliance Agamaggan - Horde Aggramar - Alliance Aggramar - Horde Ahn'Qiraj - Alliance Ahn'Qiraj - Horde Al'Akir - Alliance Al'Akir - Horde Alexstrasza - Alliance Alexstrasza - Horde Alleria - Alliance Alleria - Horde Alonsus - Alliance Alonsus - Horde Aman'Thul - Alliance Aman'Thul - Horde Ambossar - Alliance Ambossar - Horde Anachronos - Alliance Anachronos - Horde Anetheron - Alliance Anetheron - Horde Antonidas - Alliance Antonidas - Horde Anub'arak - Alliance Anub'arak - Horde Arak arahm - Alliance Arak arahm - Horde Arathi - Alliance Arathi - Horde Arathor - Alliance Arathor - Horde Archimonde - Alliance Archimonde - Horde Argent Dawn - Alliance Argent Dawn - Horde Arthas - Alliance Arthas - Horde Arygos - Alliance Arygos - Horde Aszune - Alliance Aszune - Horde Auchindoun - Alliance Auchindoun - Horde Azjol Nerub - Alliance Azjol Nerub - Horde Azshara - Alliance Azshara - Horde Aggra (Português) - Alli... Aggra (Português) - Horde Azuregos - Alliance Azuregos - Horde Area 52 - Alliance Area 52 - Horde Azuremyst - Alliance Azuremyst - Horde Ashenvale - Alliance Ashenvale - Horde
Kael'thas - Alliance Kael'thas - Horde Karazhan - Alliance Karazhan - Horde Kargath - Alliance Kargath - Horde Kazzak - Alliance Kazzak - Horde Kel'Thuzad - Alliance Kel'Thuzad - Horde Khadgar - Alliance Khadgar - Horde Khaz Modan - Alliance Khaz Modan - Horde Khaz'goroth - Alliance Khaz'goroth - Horde Kil'jaeden - Alliance Kil'jaeden - Horde Kilrogg - Alliance Kilrogg - Horde Kirin Tor - Alliance Kirin Tor - Horde Kor'gall - Alliance Kor'gall - Horde Krag'jin - Alliance Krag'jin - Horde Krasus - Alliance Krasus - Horde Kul Tiras - Alliance Kul Tiras - Horde Kult der Verdammten - Al... Kult der Verdammten - Horde
Special mention is the Darkmoon Faire Top Hat and WHEE! buff. While not always available due to the DMF being inaccessible most of the month, if you happen to be leveling when the DMF is running, it might be worth your time to go and get these. AFAIK they do stack with heirlooms, although I have not personally tested it. Fair warning: These buffs do NOT stack with each other, and the hats disappear after the DMF goes away later in the month(unless you only log in when the faire is running).
The level cap represents the ultimate goal and culmination of the leveling process, with max-level characters having gained access to all class abilities and talents, and being able to access end-game content and equip the most powerful gear. By providing an equal limit for the progression of all characters, the level cap allows for competitive and balanced gameplay in both PvE and PvP.