The above three rules held true while gearing my 59, most notably when a side quest in Bastion dropped a green reward that proc'd epic and got my legs all the way up to ilvl 158. With that said, gearing armor is all RNG. I got lucky with enough epic procs to get half of my gear to 158. Weapons and offhands are an automatic 158 from zone quests in each of the four zones, plus the ilvl 176 BoE weapons, necks, and rings we can buy off the AH. Note that only cloth and leather wearers can get an ilvl 176 BoE helm.
While the ilvl differences between 146 to 158 to 176 sound big, the stats differences aren't. Depending on stat prioritization, you may be better off with a lower ilvl item compared to higher ilvl item that features bad secondaries.
Looking forward to Dragonflight's higher zone level ceilings (and their corresponding dungeons) to level 60, it's very likely that Dragonflight 59s will follow in Shadowlands 49s' footsteps i.e. BiS will become Dragonflight gear in the high 200s, supplemented by TBC dungeons with socketed ilvl 146 gear using Shadowlands gems. That may sound like a large gap in ilvl, but 49s saw something similar between TBC dungeon gear at ilvl 57 and Shadowlands gear that ranged from 90-110.
In the end, making a 59 showed me just how broken Shadowlands rep gear was for 49s and 50s. If Blizzard hadn't placed a level 60 requirement, nearly all of the rep gear I got on my 49 would currently be BiS for my 59.