I think he's touching on a very important subject. With how the reward structure is set up right now it means that there's really no incentive for anyone to replay the content and progress their character after seeing the content, regardless of at what level you play the game it'll all be completely reset after 3 months anyway.
Here's how I would fix it (spoiler: it's linear):
- Normal/Heroic dungeons are removed, only mythic and mythic+ remain. They always drop the same iLvl loot regardless of it being a +1 or a +10, HOWEVER at the start of each reset you get a number of upgrade tokens based on your highest completed key with which you can upgrade the gear you got from the previous week to heroic raid quality. For example 1-6 could award you one token, 7-9 two tokens and 10+ three tokens.
- Remove titanforging and instead reduce the amount of loot we get from various sources in order to make the things we do get feel more meaningful. In a perfect system you'd get all the gear you want from your raid difficulty of choice a couple of weeks before the next raid comes out (on average).
- Valor points and honor points are re-added to the game and and have a cap that should net you one piece of gear per week (two pieces if you cap out both valor and honor). Honor vendors also sell upgrade tokens that cost as much as a piece of gear, you can use those to upgrade your gear to heroic raid item levels.
These things ensure that you have a meaningful and rewarding progression path through gear that isn't instantly invalidated when a new season starts. The base dungeon gear increases every season, that's your catch-up method to get you in to normal raiding. There is no overlap in difficulties and with titanforging gone there's no reason to start off a new season by clearing or split running a difficulty that's trivial to you because of upgrades. Normal mode raiders continue progressing normal from day one, heroic raiders continue with heroic and so on.