Should I use a box store for kitchen countertops?

I originally asked this question but somehow my brain wrote "cabinets" instead of countertops. I already replaced my cabinets. Now I need a countertop. From what I understand the quality of the quartz or stone is the same as kitchen and bath specialists.

I got a $4k quote from two different kitchen and bath specialists. Lowe's is $2200. I'm guessing Home Depot will be comparable to Lowe's

The kitchen is pretty simple. 96" straight counter top with a sink and two 18" countertops surrounding the oven. All with 4" backsplash.