Here's my "spin":
Relic and Mythic weapons at 75 are great for taking on 75 content.
Relic, Mythic, and to a lesser extent Empyrean weapons are great for taking on level 80 content.
Relic, Mythic, and Empyrean weapons at 85 are great for taking on level 85 content.
Relic, Mythic, and Empyrean weapons at 90 are great for taking on level 90 content.
Relic, Mythic, and Empyrean weapons at 95 are great for taking on level 95 content.
Relic, Mythic, and Empyrean weapons at 99 are great for taking on level 99 content.
Now there's a problem and that is essentially SE doesn't want us to go past level 99
(supposedly because of ascetic issues), so instead of us going past level 99 our new level 99 gear and content is actually higher than 99 (
post about levels above 99). This means Delve (non final boss) weapons that read "Lv. 99" are actually supposed to be Lv. 113 or 114 depending on how you read that list. This issue here is now the Relic, Mythic, and Empyrean weapons at 99 which are supposed to be the "best" weapons are no longer the best as they haven't been updated like in the past.
So how do the 75 to 95 versions need to be updated if they are still great at taking on content they were designed to take on?