It gets worse as you scale into epics and realize some of the things they are nerfing scale based on epic / legendary levels.
I'm most familiar with KoTC Paladin, I only ran EK a few times to cap. A 32 KoTC paladin could have the following on-hit damage, using 300 MP.
7D6 Light damage scaling with 200% MP, 171.5 damage
12D6 Law damage scaling with 200% MP, 294 damage <- scales with epic/legendary levels
14D6 Filigree bonus with no scaling, 49 damage <- scales with epic/legendary levels
Total: 514.5 per hit
Proposed changes (assuming T5 and EoL adds 2 dice, and filigree adds 1 dice)
9d6 Light damage scaling with 200% MP, 220.5 damage
Now most Filigree bonus damage isn't worth using in the first place, but included to show scaling differences since Lyn referenced we "could" use it to add 3.5 damage to our numbers.
Trying to add "Extra" dice just ends up lowering melee power / build strength and results in even lower total damage, above is best case scenario. I don't see Lyn adding 1D6 per epic / legendary to everyone's imbue dice so it's pretty much impossible for them to use the T5 without causing a big nerf.