Unfortunately, most of the hotels along Harbor no longer have a hot breakfast (a lot of them used to do a grab & go or continental and a few did a hot bfast but AFAIK none of them have brought any kind of breakfast back).
If you’re looking for cost & time efficient then getting bfast from somewhere nearest your Harbor Hotel is going to be the easiest. There is a Panera near the Fairfield Marriott & Marriot Courtyard and is an easy walk from any hotel within that same block as the pedestrian walkway (and all that is just next to the McD’s on Harbor). And McD’s does have big breakfast platter with eggs, bacon, pancakes, hashbrown and a biscuit too, so they have more than sandwiches.
The Anaheim has had a breakfast (for an additional charge) at the restaurant adjacent to their lobby, the Pizza Press. We love The Pizza Press for lunch or dinner but have never taken the time to eat bfast before the parks there so not sure the depth of their menu.
There is also an IHOP right at the pedestrian walkway and then a few doors down a Denny’s. We’ve eaten at both for midday meals or done a carry-out order to take back to the hotel at night after the parks. And eating breakfast for dinner is one of my favorite things to do anyway, so we often choose to grab Denny’s on the way back to the room at night (after having snacked instead of eat dinner to get more done before the parks close) when at DL.
In downtown Disney and at the Grand Californian there are breakfast options as well. Starbucks (that you can use mobile order for unlike the ones inside the park), Earl of Sandwich (both quick service and table service), and then at the Grand Californian you’ll have the quick service GCH Craftsman Grill as well as the character breakfast buffet at Storytellers which is the best breakfast on property, by far.
Another option is to have a few room snacks to get out the door and then eat breakfast in the parks at 10-10:30am. Red Rose Tavern (quick service) will have breakfast platters like you are possibly looking for with bacon & eggs in DL and Pym’s Lab (quick service) in DCA once lines are starting to fill up. There are also sit down restaurants in DL that have great (and not too expensive) bfast offerings, Carnation Cafe & a character buffet at Plaza Inn.
I know of two hotels that the last time I checked do have a continental bfast offering if you at least wanted to get a quick something before heading into the parks & then do one of those breakfasts after a couple of successful hours of touring. The 2 are: Candy Cane Inn & possibly Desert Inn & Suites (but I haven’t checked there in a long while). And if neither of those hotels work for you, then you could grab your own bfast items for grab & go from CVS or Walgreens (or if you’ll have a car Target down the road, or the tiny neighborhood Walmart market) to stock the in-room fridge with yogurts and possibly a half gallon of milk and then fruit/granola/cereal, just to get you out the door.
ETA: If you’re ok with staying a little further out in the convention center area (not a bad walk in & you do have the option to use the Toy Story parking lot shuttles to get to/from the parks if you don’t want to walk) some of those hotels especially the Hilton/Marriott chains might have a hot breakfast offering back.