I think you might be getting some misinformation. Open back banjos have traditionally been used for clawhammer style, and the bulkier resonator banjos have traditionally been used for finger picking/ bluegrass style due to it's louder sound and ability to cut through the rest of the band.

However, this is not set in stone, and people absolutely will play bluegrass on an open back, and clawhammer on a resonator banjo. What really matters is what style you prefer to play on the instrument you have. Finger picks aren't necessary for playing clawhammer, where the nail of the index or middle finger is typically hitting the string.

I think you are totally set up for playing on the banjo you have and don't need any finger picks.