One can argue if you should use a plectrum or not when playing the guitar. And does it even matter as long as you get the sound you want? Classical and flamenco are typically finger played and many argue that a heavy guitar riff can’t be played without a plectrum. Some guitar-kits even come with a plectrum included.
The bluesmen seem to have a different approach.
When playing with a plectrum you have three fingers left, why not use them too.
Most of the time I prefer playing with my fingers. Watch the video!