Considering the draft rate is less than 1% I doubt the breeding chances for a Legendary are much more, maybe 3% if that. I wonder if a higher level increases a dragon’s chances of breeding better stars, but there’s been no confirmation. I need to level some of them up anyway so no loss.
If you have been breeding from global launch your overall level might be holding you back. (Your hatchery won’t even let you breed 4 star dragons until you upgrade it a couple times) Breeding two 4 stars is a 16 hr wait time and 16k fish. Breeding two 5 stars means you are waiting longer and spending more, so you’ve either been spending runes or grinding like crazy to keep up those resources and cut down on that wait time.
At level 35 I get a 25% time reduction on Rare breeding, and I can hope that at higher levels there is reduced time for Epics and Legendary too. If you aren’t at a high level yet, you might want to hold off on that 5 star breeding in case the game later offers you a chance to minimize your time and turn out more hatchlings.
and to answer featherwing, if you have two dragons of the same star level, you can reach the star tier above it, although evidence points to needing a higher breedery level to hatch 4-5 stars, but I bet it is an extremely slim chance for any higher tiers. Breeding a 5 star and 4 star together will probably give a slightly better chance, with two 5 stars giving the best chance, but Legendary drop or hatch rates are always gonna be slim.