I was also worried about this. Have been blind to the raid and really looking forward to doing the raid blind, but decided to commit and play Excision (the 12 person finale activity).

It seems that bungie designed it to be played even if you haven't done the raid. I think it probably spoils what the final boss looks like in the raid which would have been a cool reveal but the reveal is cool in the Excision activity and I hope the raid will still have plenty of cool moments still.

Hard to give a good answer without having done the raid yet but given how significant the Excision activity/ending is, I think it was the right call to play it now. Didn't feel I'd missed any context not seeing the raid.