I’ve been using 4” and 3.5” for close to 7 years now. Seeing the condition they’re in, I think I will get at least 7 more out of them.
I try to take good care of them as much as possible. When I plant the starts in the garden, I make sure the pots are empty and store them nested in each other, and out of sunlight.
For root bound, I don’t know how many plants you’re growing, or if this is doable: I have a neighboor that pots up his tomatoes to 1.5 and 2 gallons before transplanting. He does get nice plants, and it works well for his 20 tomatoes he’s growing. I cannot do that with my 100-120 plants every spring, so mine do get root bound sometimes. It’s not a big deal, and they do spring back quickly after getting in the ground.