Try not to stress about every percentage of nutrition, while important, it's already gone out of the window if certain pieces are being ignored.
I definitely wouldn't advocate only giving him the pieces he likes, when considering dry mix is the majority of a hamsters intake, omitting certain pieces entirely would cause your hamster to have quite a skewed diet.
Occasionally you might find a hamster that will genuinely not eat an element of a dry mix unless absolutely necessary, but more likely than not, hamsters elect to ignore bit's of their diet in favour of their preferred pieces simply because they can do so, without going hungry.
If every morning there is uneaten food, you can probably assume that too much is being given. If you are replacing the food or topping up daily, then your hamster can happily pick away at his favourite pieces, and completely ignore the important (but less palatable!) other bits, safe in the knowledge that more will be provided in the morning. Much like if a child was routinely given a hamper of fruit, chocolate, veg and bread... how much veg do you think they would eat if they could safely await the next 'drop-off' of chocolate and fruit?
I'd personally go against manufacturers recommendations of daily/bi-daily feeding and scatter feed what seems to be a reasonable starting amount of food every few days, I'd also personally omit treats just until my hamsters main diet had settled. If at the end of this period of time there was plenty of food left-over, I would
slowly reduce the amount for the following feeds. Theoretically, as the amount of food reduces closer to levels that are actually needed, your hamster should become less fussy and you should see a more rounded ratio of pieces being consumed over time. This needs to be done with caution however, keep a very close eye on food levels (bare in mind that some is likely hidden) and be ready to provide more if all the pieces have been eaten.
Good luck, keep us updated.