Syringe filling....drip filling...hmmmm.
Tarkus as Morandir noted it's best to use an 18 gauge needle, preferably 1.5 inches in length. I prefer beveled needles since they are easier to slide into the Carto between the polyfill and the housing. So...yes, the juice is too thick for a 30 gauge.
I do believe that Juicers should know how to drip fill, but that syringe filling is the most efficient and effective way to fill Cartomizers of all sizes from a standard 1 ml to 5 ml Mega Cart. The fact that you can fill, draw back on the plunger, then quickly shoot the juice back in ensuring full saturation is a great benefit.
I rarely mention syringes when discussing vaping because some folks just don't want to use a syringe. If I had to fill 10 cartomizers I could do it in 2 minutes (it's on video) with a syringe and never spill a drop. That being said I could also do it drip filling in about 20 minutes without spilling a drop. I rarely use 1 ml cartos these days and only seem to use a syringe to extract juice from a fully filled tank when a carto dies.
Anything is better than the condom method of filling.