If it's fresh, the cause of the problem of flavourless yet astringent tea is likely overfermentation. Websites and common parlance state(s) that black tea is 100% oxidized but this isn't exactly true. The tea master monitors the fermenting piles and purely based on experience and his (or her, maybe) sense of smell decides when to heat up the tea to denature the oxidizing enzymes. If he doesn't do this, the tea gets darker but loses all of its distinctive flavour.
Orange PEKOE (OP) is actually a grade of tea and not a type. Nobody really knows where the term originated. It is the largest of the whole leaf grades. Smaller grades then proceed to op1... All the way to SFTGFOP (super fine tippy golden flowering orange pekoe) or maybe more, I'm not sure. All other things being equal, the higher grades (smaller leaves) have less strength and colour but a broader spectrum of flavour than OP.
The grades produced at an estate depends upon their picking frequency and their machinery. I have toured the Temi estate and the Glendale estate. Temi only had a handful of grades because they had a small number of sorting screens and were less efficient about picking, but Glendale had pretty much all of the possible grades and were able to sort the leaves into a dozen sizes (and even the dust by particle size).
Out of all the teas I have had, my favorite was the Glendale broken orange pekoe (BOP) which is the largest grade of broken leaf. Good, strong cup, but lots of flavour.