Not at the start while the level cap is 45, but if you go missing once we start catching up to the Asian versions then yes, you will be left behind. Simply because the lvl 50 + content starts being more strict with minimum requirements and likely the player base even stricter as they can be difficult. You can still play and still progress doing 'old' content as people will be coming and going all the time. But the gap between you and the ones who have kept playing all the way through can get quite large.
There is no telling about the community. The game isn't even out in NA yet.
Max level 45, likely have 5 HM levels above that. At 50 cap, there are 20 HM levels. Getting to 45/50 will be a breeze. HM levels is where it slows down a lot.
Yes, there is a gear treadmill. With each content update, more levels to your weapons and accessories are Blade And Soul Gold. However, you keep evolving the weapon/accessories you have, so it isn't a gear treadmill in the case of 'new update, old gear is worthless.'
i am also a very casual player and play guild wars 2, and i'm loving what i've played so far in b&s. it's a very gorgeous game, and you can enjoy the environment a lot, much like with gw2.
comparing the two, however, i personally prefer movement and combat in b&s because its really fast paced and dynamic, which is something that somewhat bothers me in gw2, especially when it comes to gw2 having no mouse-locked camera, if you know what i mean.
b&s also seems to have prettier fashion, in my personal opinion at least, the costumes are something this game really shines in.
so, yeah, i think that you might like b&s if you enjoy gw2! they both give off a very.. not sure how to put it, but to me personally, they both feel very homey, if you know what i mean? they are comforting games, the ambient does the job right. look at them casual player words lmao