Let me drop some info on Lumiere.
The first WK, the one who saved humankind and became a legend.
As the WK, he was the most powerful mage of his kingdom
Finral stated his magic is even greater than the elves, Secre stated that his magic and ability even at young age were outstanding even amongst the royals, Zagred called him the strongest mage of the kingdom and his magic formidable whilst promising to go back and fight him once he can get a body and grimoire, basically admitting that in that state he cannot defeat Lumiere, and Lumiere himself stressed his vast magic by stating that he understood at that time why he was born with such abundant magic
Worth noting is that the Lumiere we got was brought back in a pitiful state, lamented by the fact that Secre expressed those exact words as well as complained about her incompetence with the spell and wished for it to have been flawless. Still addressed as a legend.
It's also worth noting that Licht was called Lumiere's perfect equal by Secre, someone who knows Lumiere the best of all people
and Licht himself was abundantly reach in mana and magic, even further than regular mages by being an elf and loved by mana
There was a chart by Yami who gives us a view of the magic pool of the people. There is a bigger difference between Licht and Charla compared to Zagred and Licht
And Lumiere had at least that much magic. Though with him stressing that he's born with so much magic it might even be possible that he had even more.
Dark Patry, a top tier elf, further fueled by Zagred's power himself admitted that even though he possesses the same light magic and a four leaf grimoire like Lumiere, that Lumiere was on a whole entire level compared to him.
Lumiere was able to outspeed Zagred's word magic and even blitz him at times, as well as destroy the otherworldly spell that Zagred's summoned that swallowed the magic from this world, as well as again being able to react to his attacks quite easily, with Zagred himself admitting that they, Lumiere and Licht, are too fast and powerful.
Even when Zagred unleashed his full power Licht stated that his and Lumiere's magic was able to hold its own against Zagred's, individually to boost. They were then able to cast a spell together that covered the entire floating castle and protected everyone from the influence of Zagred's magic. Lumiere himself stated that his magic can stand against the devil's. And the magic they sent not only healed but also powered up people such as Yuno. Note that incredibly powerful individuals such as Salamander Fuegoleon were utterly hopeless against the spell Zagred cast while the two were able to protect themselves as well as all others there from it.
During his battle with the Devil Licht, Licht lamented that only Lumiere will be able to kill him
When seeing the appearance of the devil Licht people were already claiming that it is the end of the world
During his battle with the devil Licht he was able to match its attacks as well as showcase his speed by dodging it
When devil Licht used by a huge chunk, if not all of his destructive power, only then was Lumiere questioning his ability to block it and had to rely on magic items to absorb the magic a bit
In the end he managed to defeat the devil Licht, albeit with Licht stopping himself, however the destructive potency Lumiere's attack showed is tremendous, stretching far and away and wiping out Licht's body leaving only a skull
It could be argued that it rivaled the attack that Licht used to eradicate Zagred, although Licht had to borrow power from his fellow elves
It's also worth noting that Lumiere had to expand magic just to keep his body from falling apart at all times
Truer words have never been spoken.
