It's a common misconception that the top of the filler should always look like it did after fully priming it.
A perfectly functioning cartomizer in a cartotank will have a dry-looking upper filler after vaping on it several times, even if it was properly primed to begin with. Look at the below diagram that I made to allow me to illustrate this point:
As you vape, juice is drawn down from the top of the filler to the bottom of the carto by suction (negative pressure). Juice from the tank is also drawn into the carto through the carto's holes by the suction, both illustrated by the red arrows. The tank will never keep up in keeping the carto and its filler completely full, but it doesn't need to. As long as the filler around the heating coil stays wet, there will be no danger of the filler becoming burnt.
As I have noted elsewhere, Boba's Bounty presents a tough challenge for any wick device (carto or clearo) because it is so thick, and also because it contains a lot of particulate matter in it. This causes the wick material (filler or silica string) to become clogged and therefore not wick the juice adequately. It doesn't matter much how many holes you use or how large of holes you use in the carto, as that's not the problem. It's the thickness of the juice and the particulate matter that clogs the filler or strings.
Your best option to vape Boba's is to use a drip atomizer or a bottom feeding mod using a drip atomizer.