Let's say there are 2 grocery shops. All their costs and expenses are the same but one grocery shop sells twice as many products per square foot / unit of time.
As someone interested in more profit, which store would you rather own?
The argument you're responding to wasn't "Tesla's stores are dramatically more efficient".
The argument is that Tesla stores sell Tesla's EV cars effectively (because that's the only thing they sell) and traditional dealership anti-sell EV cars because they make more money on selling ICE cars.
This is not a conjecture. In addition to plenty of anecdotal evidence, there were qualitative studies both in US and Europe where researches sent "mystery shoppers" pretending to be interested in buying EV cars.
The results were dismal. Many dealerships didn't know much about EVs themselves and in the worst case, they would literally lie about how bad EVs are.
That will be a problem for GM, Ford, and others when they finally have good EV cars to sell.
And there's no obvious solution to that. Car makers and dealerships are frenemies so it's not like GM can dictate terms to their dealers or that they can force dealers to do a good job selling EVs.
The obvious solution (heavily subsidize dealers with bigger discounts) is bad for profit margins. Investors like profit margins and it'll look doubly bad because when they finally have EV cars to sell, they'll go through the same "loss due to low volume / production ramp" that Tesla went through in first half of 2018 and will be competing with Tesla's 2021 heavily cost optimized production.