Sugar content is always high in muesli because of all the dried fruit. As mentioned before, buy a muesli base and add nuts and seeds to it, with no dried fruit. That’ll reduce sugar content considerably.
In truth you want to avoid mueslis that have a high wheat content and go for ones that are mainly (or solely) oats. Then add milk and give them a couple of minutes in the microwave as the heat makes it easier for the body to break them down and absorb the goodness (you could just have porridge of course).
To suggest that muesli for breakfast is not healthy is, frankly, bollox. It is pretty much proven that oats lower cholesterol and blood pressure and that they are an appetite suppressant as they are a slow release carb, thereby keeping you fuller for longer. Have some eggs each day as well for sure, but eat oats as well!