I'm no expert... just sharing my own experiences.
Those two boot styles are not alike at all...
Touring
Motocross
Motocross boots are more like track boots, but with greater emphasis on shin protection. They're much higher. I also think they may have less emphasis on ankle stability, but not sure because I don't ride dirt... a lot of high-end track boots are more like ski boots than anything you can walk in.
Touring boots offer similar coverage and ankle support to work boots. They differ in having stiff plates over the shin, shift protectors on the toe, soles that are better suited to motorcycle use, etc. You want to be able to walk around in a touring boot all day long, so they never have exoskeleton-like ankle support or anything like that.
The whole "what's enough?" question is tricky. Just like protective gear, it's a compromise between the protection you get and real-world utility. My track boots are utterly unsuitable for daily wear because walking in them for more than a few hundred yards starts to get painful. But my street boots are all-day comfortable. You know me... I'm ATGATT, all-leather. Far more conscious of this stuff than most riders. But I wear cheap touring boots on the street.
Break this down and think about it. What does a boot need to do?
- Stay together in a crash, just like any piece of protective gear.
- Protect your shins from the odd flying rock.
- Offer ankle support if you go down.
- Be compatible with the controls of your bike (i.e. heavy lugged soles can catch on your pegs and make shifting foot position awkward, shifters can scuff the toe box, etc.)
- Be practical (walkable, comfortable) in the real world.
Judge a boot that way.
My thinking is that while a high-end touring boot will be of undoubtedly better construction than my cheap ones, the chances of me actually sliding along with my feet under me are small. So the "stay together" thing is different from the garments that protect my torso and legs.
Ankle support is a clear trade-off. You can wear massively braced boots that you can't walk in and feel secure that your ankles will be okay... but what's the point if you can't walk around when you get off the bike?
Protection from stones is easy. It's just plastic plates in the shaft of the boot.