I am not sure the exact caps of what weapon damage used to be, but I do remember Obsidian Lances being the best tier 20 weapons with an attack range of 88-100. So being that a tier 20 weapon was 100, I think you could have weapon tiers be gauged by max damage as they were be the easiest thing to do.
Tier - Max damage
1 - 5
2- 10
3 - 15
4 - 20
5- 25
6 - 30
7 - 35
8 - 40
9 - 45
10 - 50
11 - 55
12 - 60
13 - 65
14 - 70
15 - 75
16 - 80
17 - 85
18 - 90
19 - 95
20 - 100
21- 105
22 - 110
23 - 115
24 - 120
25 - 125
Then if you adopted my idea of skill allowing wielding weapons above your tier, you could add tiers 26-30 of weapons, scaling them by 5, and having tier 30 weapons being essentially only being able to wielded to full by a 25th tier Grandmaster and have a max 150 damage.
Those may have even been the original Nexus tier caps, or close to it.
I think before, you also could wield weapons above your tier, if you were one level under, it would say something like, You can’t quite wield this weapon to its full potential, but you still hit for like 75% or 80% of the damage, which made it not much worse than using a weapon of your tier. But if you were two levels under the tier cap, you hit terrible with it, like 30% or something.