The big question there is why these metalworkers showed up in only one part of the empire, one of the less wealthy regions, and not one with some unique needs for bronze casting. Note that these are cast bronze, using the term "metalwork" conflates smiths who work with tin, gold, bronze, and iron, but those were different professions. This isn't a blacksmith showing off his ironworking skills, it's a person of a different profession casting fine bronze. Hard to say why you'd have mendicant bronze workers casting things, I don't know of any records of but it's a very limited area for so many finds, while this same work was needed all over the empire, why nothing in Spain, Italy, North Africa, or the eastern provinces where they'd need the same? Why just that one highly restricted range within Rome that coincides with Gallia and Britain?
I have always thought that if they were candle holders it would make perfect sense. And they would be much more needed in the northern part of the Roman Empire than southern. And this is why no accompanying materials have been found in the dirt. Because wax is malleable and would disintegrate over time.
But yeah why would they have ever gone to the south?
You don't need 12 holes of varying sizes to hold a candle, and these would have been disproportionately expensive to make for that role.
The problem is that one can poke similar holes in other proposals. Personally I favour the "proof of skill" explanation but there are also arguments against that.
The Romans mostly used oil lamps rather than candles, the use of candles as a popular light source developed among early medieval Christians who started to use them in their churches after the olive oil supplies dried up in the late/post Western Roman empire. These were too early to be tied to candle use (and strangely distributed geographically). Also the Romans had no kind of industrial standardization or production, every candle was hand made and unique, all the wax/tallow was valuable, so the later Romans who would have used candles would have used a candle holder designed to capture any lost fuel to reuse.
