I think all hamsters have a preference to which food pieces they prefer but as long as they're healthy, they're probably eating more of the other pieces than you think.
All of mine are fed on Burgess as well as occasional fresh veg, oats/porridge, dried mealworms (not too many because Burgess already contains them), pumpkin seeds, and they also occasionally have those dried leaf and flower treat mixes (I can't remember the brand I have, but check the ingredients because some aren't hamster friendly). I agree that Burgess looks quite plain but it's the best food for them and I think that if you're worried about what he's eating it's better to supplement the food rather than change it completely.
Are you removing the corn/peas from Burgess? Unless your hamster has developed diabetes you shouldn't need to remove these otherwise it will lower the nutritional content in the food. He'll be fine eating them, don't worry
If you try Harry Hamster you might need to break the biscuits into smaller pieces so they're more manageable, mine wouldn't eat them because they were too big. The whole corn pieces are also very hard for them to eat because of how hard and smooth they are mine couldn't actually bite into the corn (though you could probably remove these because there's still the corn flakes?).