Fumanstu Getting ‘Beyond Light’ will get you a certain amount of stuff yes - and getting it for free is a lot better than paying what Bungie are asking for it, which IMO is about 25 quid too much. But to get ‘all’ of Beyond Light, you’ll also need to get the Beyond Light season pass, which I suspect - unless something explicitly says so - isn’t included in the gamepass deal. You’l get more stuff than the F2P player will get, but I suspect you’ll get less than you might be expecting.
I know this is true on Playstation but I can’t check on Xbox - on the store are there several versions of Beyond Light for sale? I suspect there’ll be ‘beyond light’, ‘beyond light plus season pack’ and ‘beyond light deluxe edition’ (which is basically beyond light plus season pass plus some real world tat for about 200 quid). What Gamepass peeps will get is very probably whatever’s listed in the basic edition.