Pretty much what Gegenji said. There's no reason those two disciplines have to be mutually exclusive - they aren't drawing from conflicting power sources, they don't both take a ridiculously long time to learn, neither is limited strictly by political affiliations. I don't see any reason why your character can't pursue both.
But - DRK - as in, soul crystal, I̷̴͢NÌ´Ì´Í Ò‰Ì¢N̵̛͜E̸͘ÍRÍ¡Í€Í Ò‰AÍŸÍ¢B̸̶͢͞Y̶̨̢S̷҉̧SÌ·Í̴̸, etc - is kinda a big deal, and PGL is just "being good at punching stuff". This makes them easy to co-exist (it's not like it's two big deals competing for screen-time), but also means if you play DRK straight, it's likely to end up overshadowing your PGL class by quite a long way. Like Valen said, if it's just the greatsword you want - not a fundamental direction-change to the character and their development - there's no reason you can't do that without having all the extra stuff that comes with the DRK job as a whole. And like we all said, there's no reason that can't coexist peacefully with a PGL proficiency - maybe moreso than if you take up the entire DRK job, since it'll just be a character who's good at two types of fighting (maybe blending them together?).
But if it's the extra stuff that appeals to you... go for it imo. Just make sure you give it the time and effort it deserves - don't half-ass it, or it'll come out flat. Here's my transcription of everything about DRKs from the lore book. There's more lore scattered throughout the in-game quests, but I warn you to take everything in the 30 to 50 story with a grain of salt, and focus on the 51-60 and lore book information for objective truths about the job.
But - DRK - as in, soul crystal, I̷̴͢NÌ´Ì´Í Ò‰Ì¢N̵̛͜E̸͘ÍRÍ¡Í€Í Ò‰AÍŸÍ¢B̸̶͢͞Y̶̨̢S̷҉̧SÌ·Í̴̸, etc - is kinda a big deal, and PGL is just "being good at punching stuff". This makes them easy to co-exist (it's not like it's two big deals competing for screen-time), but also means if you play DRK straight, it's likely to end up overshadowing your PGL class by quite a long way. Like Valen said, if it's just the greatsword you want - not a fundamental direction-change to the character and their development - there's no reason you can't do that without having all the extra stuff that comes with the DRK job as a whole. And like we all said, there's no reason that can't coexist peacefully with a PGL proficiency - maybe moreso than if you take up the entire DRK job, since it'll just be a character who's good at two types of fighting (maybe blending them together?).
But if it's the extra stuff that appeals to you... go for it imo. Just make sure you give it the time and effort it deserves - don't half-ass it, or it'll come out flat. Here's my transcription of everything about DRKs from the lore book. There's more lore scattered throughout the in-game quests, but I warn you to take everything in the 30 to 50 story with a grain of salt, and focus on the 51-60 and lore book information for objective truths about the job.