For me the spaniel’s primary function is to hunt for, and find, game. The retrieving is just a sideline after the fact, so to speak,

and since I only shoot over my dogs, most retrieves are pretty straightforward so don’t need much in the way of refined handling. So when I worked springers, and later cockers, I based most of my training around hunting. Dummies were thrown partly as steadiness training, rewarded by completion of the retrieve, or left as a memory retrieve while the dog was hunted on and sent back for it later. This developed into surreptitiously dropping a dummy while the dog was hunting then sending it back for it as a blind retrieve.
Back in the day I relied heavily on corrections and would run down a pulling dog that was sloppy on its turns and give it a good scruffing, which was the norm back then. These days I don’t use corrections and so would revert to game play, sneaking in a dummy or ball and then redirecting the dog onto it to find, and this would have the dual purpose of building a strong working relationship between me and the dog, where we begin to build trust in each other, while giving the dog purpose to stick with you, because good things happen around you, and providing it with a motivation to hunt close. At the moment it is pulling because nothing is happening around you so it hunts on looking for environmental reinforcers, which are more readily available. I also used to hunt my young cockers trailing a 15 to 20 m length of thinly braided chord that snaked about in front of me and which I could quickly step on if things went awry. Your young dog should be hunting within 10-15 yards either side and in front of you (even tighter if they have been allowed to pull on) at this stage and if you stopped walking should continue hunting just in front of you rather than pulling on. If they’re too focussed on the environment then they’re not going to be engaged with you and things will go wrong and you’ll be forever hanging onto their shirt tails.