1) Yes but...
2) Penetration, accuracy, handfuls of cash, and reliable function.
External ballistics is more complicated than a single number.
First, I think energy figures aren't generally useful except for when comparing entire classes of cartridges, and this is particularly true for pistol cartridges. I think momentum is generally a more useful figure, as momentum of similarly constructed bullets appears to more closely mirror performance. Even disregarding the construction of novelty cartridges, the low mass/high velocity rounds tend to have relatively low momentum. Note that this is the flip side of the claim of low recoil.
At any rate, it's physics. Lazily stated, energy = (1/2)mv^2 . A small increase in velocity makes a huge increase in energy, even if mass has to be decreased to do so.
How do you decrease the mass of the bullet while maintaining the same diameter and overall length? By grossly compromising its construction.
With Magsafe cartridges, the bullet is a copper jacket full of glue and a maybe a dozen birdshot pellets (depending on caliber).
When it hits, the first couple inches of the wound cavity are hamburger, and then the least deformed birdshot pellets make a few pinprick tracks 6-7 inches out.
That's grossly inadequate, and in naked boneless gel at that But that's the (original) purpose of prefragmented rounds. To limit penetration.
Except, in the real world, if the round hits drywall, it's not uncommon for the cavity to clog or the nose cap to crush shut and then perform not unlike a lightweight FMJ.
It's also difficult to uniformly distribute the glue and birdshot, so the rounds also tend to be unbalanced and offer poor accuracy. It's not really a problem at self defense distances, except one thing to note is that the rounds tend to shoot low due to the high velocity.
Also, to get the super lightweight bullet up to speed, they need to use super fast burning powder. This generates a screwy pressure curve outside of what pistols are designed for. This, combined with the Magsafe's generous nose cavity, is not unknown to cause reliability issues.
Magsafes/Glasers are ill considered novelty rounds, and are generally unsuitable for defense outside of a few edge cases. And maybe even then.
I don't really know anything about Grizzly or RBCD. I seem to recall that Grizzly's conventional loads are reasonably well regarded. The Grizzly Extreme appears to trade penetration for expansion, with one Youtuber comparing the wound track to that of a broadhead arrow. It performs unpredictably if it hits anything else.
https://www.youtube.com/watch?v=t_3VYszyyNU
I've never even heard of RBCD. A quick google pulls up the Box O' Truth, which suggests that their rounds are indeed the standard prefragmented nonsense.
http://www.theboxotruth.com/the-box-o-truth-38-rbcd-ammo-vs-the-box-o-truth/