I think the reason there isn't any matchmaking is because they aren't really that difficult to complete solo. I've faithfully done every daily heroic solo since level 16 dying only once if at all. The weeklys are a tad bit more difficult but nothing a fire team with 2 level 12s couldn't fix. The first weekly I'll admit felt almost impossible against Sepkis Prime, and needed guardians of the same level or higher to complete. But this past weeks surprisingly was a lot easier than the first time I fought Phogoth. I'm not disagreeing with you I'd prefer the matchmaking, but it's not really a necessity, and Bungie could possibly feel the same.