Well a dyno tune will do A/F ratios. Have you noticed most tuners let the car run on the dyno first? Most say it's to warm the engine up. In reality if the tuner is good, he is checking A/F Ratio and seeing what would be beneficial to you. That's why any good tuner should ask questions while tuning a customer's car.
Exactly, dyno tuning is very limited. I would never rely on just a generic dyno tune. Most those tuners have a stockpile of tunes they keep on file. It makes it quicker to get a car into a safe operating range. They will take into account the mods to the car & drop a generic base tune into it then tweak what few parameters they can on the dyno to get a safe A/F while tryin to impress a customer with HP numbers. Plus a dyno can only load a certain way, they dont have variable loading like driving down the street. And not even all the dyno shops have units equipped to run loaded. Hence the difference in numbers people get from various shops using different dynos (like a Mustang dyno vs a Dynojet). A street tune is just much more in depth. But alot of people just really dont know and assume all "tunes" are the same as far as method to final result. I'll stick by my thoughts on dyno vs street when it comes to tuning. I'm not sayin the dyno isnt a good tool but there is better. Another factor would be the cost of laptop, good wideband sensor & gauge, tuning software & hours of tuning to be able to do a solid street tune. Alot of people arent willing to spend the money or just cant so a $4-500 dyno tune session is the best option for them. To get the absolute most out of a tune though you need live data logging with real world loading situations. but unless you know someone getting one done is far from cheap usually.
And honestly if your in a area with shops like Vengence, RPM & so fourth that have some of the top tuners they have enough tunes on file & tuning experience they can get you where you would be with a full street tune on a dyno & save you some money. But thats far from the case around here unless you wanna trailer it somewhere. Hell around here findig a shop or dyno tuner with enough LS engine experience to trust is hard to do without driving at least 2hrs away.