I actually had just asked this question recently on a thread because we bought our Titan through a breeder. He had him on royal canine as well(and really talked up the brand of food:which seems to be the theme with breeders and royal canin) and titan seemed to love it,had no allergies but we felt it wasn't that healthy for our little guy. A lot of feedback was that royal canine is definitely not a healthy choice especially in the long run because it has a lot of fillers that aren't nutritional. We are currently integrating Fromm brand (4 star) and it's amazing! It's extremely nutritional with no fillers and all ingredients you can actually understand lol. We love it for him and he loves it too.
Just be careful if you do decide to change the food. integrate it slowly.it'll probably take about a week to fully do it. Each day increasing the amount mixed in. That way it wont upset your bullies tummy or cause stomach issues.(check poop)
Also be careful of allergies because some bullies can eat some brands while others can't.
i've read on here as well that some 6 star brands aren't necessarily the best because it's based on all breeds vs specifically for bulldogs. I def like the FROMM brand so far. It is expensive but it makes Titan happy and healthy which is most important. We order ours through petflow and it ships very quickly and the prices are cheaper than driving to a store that actually carries it (they don't charge shipping on product over $49 and there is no sales tax as long as u don't live in three states which are listed on their website)
hope this was helpful and sorry so long just want to inform you as much as possible. good luck..feel free to ask anything!