Royal Guard is definitely good, and will help for a certain Spider 20 team, yes - but you've a long way to go before getting there. That said, I do think he'd be a better fit for your Dragon 20 team than Kael, so, yeah I think he's probably worth investing in. Spider is okay, but I wouldn't bother with her for now. Tomoe is pretty much trash, ignore her.
PS - you really shouldn't be using shards just on any random day. Save them for fusions.