Federalism Is Not a Cure-All
But Abbott isn't defending the 2nd Amendment. S/he is ignoring it. Saying that DC should be free to ban arms because of the crime situation nullifies the individualist interpretation of the 2nd Amendment -- if I have a right, that right exists even when it's inconvenient, as speech and criminal rights often are. I doubt that Abbott would consider applying federalism to the 1st or 5th Amendments; we're not going to let states "experiment" with mandatory prayer or the Miranda warning. I'm not even sure DC would permit a collectivist interpretation of the 2nd Amendment, for example allowing a militia to form and store arms for use in an uprising against tyranny/ invasion.
I lean collectivist myself (1, 2), and find the hunting and personal self-defense rationales of the NRA wholly irrelevant to the 2nd Amendment no matter how practical they are. But I don't think advocating that gun policy to be determined at the local level, without setting some floor of what the 2nd Amendment does require, can be called "defending" it.
Federalism may be a good structural idea, but it's an appalling way to maintain our rights -- it's often easier to collect a majority in a single state to oppress a minority than it is to collect that same majority nationwide. Compare the success of state constitutional amendments banning same-sex marriage with the failure of the Federal Marriage Amendment. If I were the type to hang out at ranges and to display pictures of myself with gun in hand, I would be happy with the federalization of the 2nd Amendment, as long as it was done by the judiciary upholding my rights, like the 5th Circuit in dicta. The recently expired "Assault Weapons" ban was controversial partly because of its sheer silliness. Instead of focusing solely on the ease with which a gun could shoot many people (features like automatization and magazine capacity), it worried about the stock and pistol grip, and whether there was a grenade launcher  or bayonet mount. But federal gun legislation dates back to at least 1934, and though the National Firearm Act's regulation of fully automatic weapons was challenged at the time in U.S. v. Miller, it doesn't seem to be much of a rallying cry nowadays.
Incidentally, Hey Abbott's citation of the Wisconsin hunter who killed six others left out a fact that might be relevant to the attempt to identify factors that have increased mortal violence: quite likely, "increased social competition, stress in the workplace, urbanization, rapid growth, and the destruction of our social safety net have prompted our violence crisis," but another possible element is the diversification of American society. The Wisconsin hunter in question was Hmong Laotian, one of the less "model minority" Asian groups in the U.S. whose large-scale immigration after the Vietnam War was forced by their cooperation with the U.S. in Southeast Asia, and subsequent targeting by Communists . The 2004 killing has been considered as a cause of the recent murder of a Hmong man by a white hunter. Hey Abbott appears to be most concerned with people going "berserk," committing "atrocities" and "countless school and workplace shootings," rather than the commonplace gun murders connected with sex, drugs and money that I would bet make up a far higher proportion of gun violence.
 Hint to Congress: ban the grenades.
 Much of the "model minority" myth about Asians stems from immigration cherrypicking. Unless it was feeling guilty about the possible genocide of a group it had used and then abandoned in foreign policy (and you can't give everyone a no-fly zone!), the U.S. government was quite selective about the Asians who were permitted to immigrate, often requiring that they already speak English, be well-educated and have skills of which America was in need. There's a reason that a disproportionate number of South Asian-Americans are doctors and engineers -- the subsistence farmers rarely got visas.