In order to make the ultima weapon in the first place, they had to use the "Eye of SABEK" and repurpose old tech to make the weapon work and do what it does.
The newer weapons, while they can't consume primals by themselves, (perhaps because they don't have space to store it within the eye?), you have to admit that level 80 machines are more powerful then the level 50 ones...
Perhaps any one of the EX trial versions could take down the UWU version.
Lets set that to one side though. You notice that when Gaius van Baelsar uses the stolen power infused into himself to go limit break, he changes not just himself, but his weapon and his armor.... but not the ultima weapon.
Look to emerald weapon, when the limit break happens, when the data is poured into it, the limit break not just powers the weapon, not just the armor, but the entire weapon goes full super saiyan golden god glow.
Sure, these new weapons can't cast ultima at a level that could wipe a nation off the map, but UWU couldn't either, without the eye, so we can't credit THAT power to the Garleans...
... but what we CAN suggest that they've done, they've learned to do even better.
And diamond weapon implies they've nearly perfected it. R,G,B,Y, are test beds, diamond the final prototype... now what?
(also of note, there's 2 different proto ultima's out there to concider what they might have made without the eye, just themselves with salvaged tech)