Squats and deads are as much of a full body exercise as almost anything out there. Back squats are hip/ham dominant near and below parallel, and quad dominant above parallel. One of the reasons that squats may not provide the same amount of quad stimulation as something like leg press is weakness in the hips and hamstrings. If you can't get out of the hole, you can't squat the weight. The quads have much better leverage in the top half of the squat then the hips have in the bottom. Bring your hips up to par and you will squat more; and grow more. I get more lower body strength from squats than anything else.
Change in any routine is good. When you change from one exercise to another there is a learning curve for your muscles and you will make quick gains in the beginning. You might try front squats for a while. They are more quad dominant than back squats. Go with higher reps: 4/5x8 or so. Make sure that the last rep is the LAST one you can do. Follow that with SLDL and let me know how that works.
DOMS isn't a real indicator of growth or growth potential. It is a sign that you beat up your muscles, and it is easy to use soreness as an indicator (I do it, too), but being REALLY sore doesn't mean you're going to get REALLY big. When I do a true powerlifting workout, I gain strentgh faster than with any other workout, but I get nowhere near as sore. DOMS can be controlled (to a point) with things like fish oil, prehab and rehab practices, and some people even say that glutamine helps reduce it. Mostly, some people get it and some people don't.
Full deadlifts are hip and back dominant. You don't pull as much of your quads into deadlifting unless you lift deep (off pads or blocks). I hate deadlifts. They are brutal. If you aren't getting anything out of deadlifts, then you aren't doing them heavy enough. This isn't a high rep exercise. After 10x3@385, I am dead. Exhausted. I am famished all day long. I can't eat enough. I get sore from the back of my knees to the back of my neck. I would say that there isn't a more effective exercise for full body work than deadlifts.
I do deadlifts, t-bar, bent rows, good mornings, pullups and downs...all of it. Not all on the same say, mind you. I may be crazy, but I'm not insane.
I think that big, heavy exercises really suck. They are hard and they make me sweat and breathe heavy. Sometimes I get nauseous. Also, they make me bigger and stronger.
If you don't do squats and deads, will you wither away and be weak your whole life? No. Can you get bigger and stronger without them? Yes. But you're going to get bigger and stronger faster if you use them in your routine. They can be two of the most useful exercises in your arsenal.