Interesting points, I definitely see what Gr8_EE8 is saying. Quite frankly it makes sense, and I too don't need to justify my position but I know a thing or two about working on cars.
Another point that should be kept in mind is that the vast majority of times, a rounded off nut/bolt is caused by you not holding the ratchet at or close to a 90° when you're using it. It doesn't take being off much before you have essentially no contact patch between the socket and the nut/bolt, hence it slipping and rounding it off. I don't have a protractor but you get the idea.
Using an extension makes it even more difficult to hold the ratchet at that 90° angle, but with that being said a shorter extension doesn't give you as hard of a time as a longer extension will. That's just physics.
In all of my wrenching I have yet to round off a nut or bolt with a 12pt solely due to the fact that it's a 12pt. It has always been because I was either a.) holding the ratchet/extension/socket at an angle far off from the ideal 90°, or b.) I was trying to loosen the nut/bolt with a 'drive' that was too small.
For example, if a 10mm bolt is very tight, and you try to loosen it with a 1/4" drive ratchet, you don't have much leverage since the 1/4" ratchet has a handle that's maybe 4 inches or so long. It's easy for you to try to tighten/loosen the nut/bolt so hard that your hand just slips off of the ratchet (due to the short handle). This is going to cause whatever you're working on to round off.
If you instead take the time to use a 3/8" ratchet on that same bolt, you will find that the longer handle makes the entire process much easier. When you apply a large amount of force, the nut/bolt will actually loosen/tighten instead of simply rounding off. The added rigidity of it being a larger drive and the beefier extension/socket also contribute to the process being easier. It goes without saying but this principle also applies to using 3/8" drive vs 1/2" drive ratchets/extensions/sockets.
Yet another point I'll make about sockets is that the size of the socket is not very 'true' when comparing low quality tools (harbor freight) with average quality tools (craftsman, kobalt) or especially high quality tools (snap-on, etc. etc.). From my experience at least, low quality tools have always have a 'loose' fit. Best example I have is a 17mm wrench, as that's what's used for Honda oil pan drain bolts - assuming you don't have an oversized oil drain plug.
If you use the 12pt end of a 17mm harbor freight wrench, craftsman wrench, and snap-on wrench, it is extremely clear that the snap-on wrench has the most 'snug' fit. While the other wrenches will fit the bolt and work fine, they have a much more 'loose' fit (especially harbor freight). This loose fit is due to a number of things such as manufacturing tolerances, but point is that the loose fit results in less of a contact patch between the wrench (or socket), and the nut/bolt you're working with.
This smaller contact patch results in you applying force that may not necessarily be at or close to that 90° angle mentioned previously, and when you apply force that's far enough off of that angle, your wrench/socket slips - resulting in a rounded off nut/bolt.
As far as tools, I agree that snap-on is overkill for what most of us on here will be doing; the majority of my tools are craftsman and harbor freight. If you use the correct 'drive' (1/4", 3/8" & 1/2") for the correct application, you really have to try to break the tools. Obviously cheap, low quality tools like harbor freight will be the first to break but so far I've had decent luck with them. If you don't have room to use the next higher up 'drive', then the easiest solution is to get a ratchet with more teeth. Only downside is that these high tooth ratchets are more expensive than your typical ratchet, especially if you're getting a higher-end brand like snap-on.
This is simply what I've learned over the years.