Unfortunately it's legal, they will probably have clauses in the terms and condition to cover this. Just nobody can be bothered reading them. I do feel for you though. Bungie could have done a much better job with supporting legacy content. They could just have different difficulties in the daily and weekly content. Just with legacy rewards. The only time they need to increase the level for those is when they increase the level cap for legacy owners. If you can get the funds together though I highly recommend getting TTK. The story telling is much better and the NPCs actually have personalities and are not just people telling you "go there, kill this dude, come back, go back, kill another dude"