I always think the consumer having more choices is a good thing. However, given that the only difference between what O'Reilly sells and what Napa sells is the sticker on the box, the price, and if it's in stock, I'm not sure how much it even matters.
I do think a fully corporate model has many advantages to you, as a customer, over a franchise model. Remember that in a franchise, the business owner is Napa's client, not you - you almost don't matter to Napa. On the other hand, when you shop at a corporate location, you're their customer. In theory this means you'll have a more consistent experience, inventory management will likely be better, issues are easier to resolve, and it could even lead to better pricing.
This whole thing goes beyond auto parts though... For example, McDonald's is NOT in the food business, they are in the real estate business. We bought our Equinox EV from the Chevy dealer, not GM.
On the other hand, it also means individual stores don't have the flexibility to customize what they offer. For example, I've heard of franchised Napa stores carrying AMSOIL... something a corporate store couldn't. Also, the owner of a Napa store has more power to go above and heyond than the typical manager or even district manager of an O'Reilly.
Anyway, O'Reilly DOES have a franchise program. It's called Parts City. Never seen one IRL and I think there are only a handful around the country, but the direction I think it could go if they end up acquiring Napa is that they take over the corporate owned Napa stores where it makes sense and spin off the franchised ones that either redundant or where there are anti-trust concerns into something else.
Napa or not, there does seem to be a push to increase O'Reilly presence in heavy duty, ag, fleet where Napa has traditionally been stronger. I think in a world where rapid cost increases and supply chain issues are probably the biggest concern across many industries - auto parts, computer chips, minerals/"rare earths" etc. a company like O'Reilly might be able to weather that storm better than Napa can.
In the last decade so many parts have been transitioned from name brands to store brands. In many cases the part inside the box is the same (although oftentimes it's not). But when you are selling a Murray idler pulley, you can buy it from whoever you want. If you buy them from Gates, if Gates wants too much money or doesn't have any, well, just buy them from Litens. Litens doesn't have any? Well, find some random Chinese supplier - as long as it works, who cares. And even if it doesn't last more than two years, it's OK... that's what the warranty is for. Napa does have an advantage here because they already mostly sold store brand stuff.
The funniest thing is still the recalls where the recall is because the part came to the auto parts store in a Napa box. Even though, well, I don't work at a Napa auto parts store. Just makes me laugh because of how many hands the stuff had to pass through to end up stocked on the shelf (even if it's in the back of the store). You don't need to be an ASE certified mechanic with two decades of experience to realize that probably doesn't belong there.