But the basic technology behind LTE and LTE-A is the same. LTE, whether "3.9G" or "4G" is still significantly more spectral-efficient than UMTS/HSPA, which is the older 3G network that T-Mobile successfully petitioned to be deemed "4G." In a lab, yes, HSPA can get speeds of 14.4Mbps or 21Mbps, but in the real world, LTE significantly outperforms HSPA.
Right, I've used T-Mobile's HSPA+, and it isn't nearly as fast as their claims. I've never exceeded a few mbs per second, let alone getting anywhere near the theoretical 14.4 - 21Mbps.
In real word use, it's barely faster than Sprint.