There is a lot of grief, anger, hate, and sorrow at what happened - but like with other similar events, can this sort of thing be prevented - are there solutions or are we stuck on blame?
Minimized and reduced, surely. "Prevented?" Only insofar as the minimization efforts prevent individual events, such as the one prevented last weekend in Los Angeles. And therein lies the dilemma. The ways and means used to identify, detect and interrupt a whole host of violent acts and perpetrators -- terrorist or "simple" -- need to be kept secret in order to be effective.
Of course, the would be perpetrators of those deeds do know they were thwarted, but they often don't know precisely how, except, of course, if their plans and planning methods allow only one or two possible means of detection. Thus, we, the innocent observers, don't generally become privy to the actual nature and extent of heinous crimes that our government has successfully interdicts; however, when it's obvious to both our security forces and their opponents just how and why we were successful, sure, either side can let everyone else know about the halted violence.
The dilemma above leaves folks outside the "need to know" circle of professionals with an additional quandary of our own: can we content ourselves with the presumption that our government is doing the best it can and that as non-experts or "insiders" with access to "secret" information on matters of crime, terrorism, violent offender psychology, etc., we should rely on our government's attestation that it's doing the best it can to combat violence like the "Pulse" massacre? Sure we can with hindsight criticize and talk about what should have been done, but so can the folks who are charged with doing the best they can to prevent "whatever" from happening. In my experience, prior to an event's occurrence rarely has there been any plausible and practical basis for having done (or not) "what should (should not) have been done."
Terrorism, even though we don't have a precise meaning for that term, aims to refute the primary objective of state security agencies and employees. The fact of the matter in my mind is that it's preposterous to expect our security organs and personnel pragmatically speaking do more than provide and ensure a general climate of security and safety. Terrorist acts and terrorists aim to erode the polity's sense that it is, in general, safe. The reality, however, is that, in general, in the U.S. we are all quite safe, even though there may not be a specific and absolute level of safety one whereby it's assured that, say, when we go to the mall, that mall won't be a target of terrorist violence.
The U.S. has literally millions of soft targets, some are heavily peopled, like malls, bars and nightclubs, and so on, others are not, but are critical to our infrastructure and to our way of life.

Ask yourself this: do you prefer terrorists hit a bar somewhere and kill 100 people or take out the sources of electricity for thousands of people for months at a time? And good luck catching the bomber who destroys major elements of our electricity transmission infrastructure.
It's great to see the public uniting behind this, but why did it take this one event when violence against gays, even murder is nothing new here?
Hard to say. The cynic in me thinks it's a matter of the context of the "Pulse" event being one that inspires a choice between gay issues and terrorism issues. Certainly from my own POV, gay folks, in and of their being gay, pose no threat to me at all and on no level at all. In contrast, angry and would be violent individuals, gay or not, most certainly can and do, and they can and do at the most critical levels of all, that of my quality of life as well as my life itself.
Lone Wolf Attacks and the Problem with Prediction:
Questions - if Mateen hadn't been radicalized by Islam, would he have found some other reason to commit these murders?
You may find some of the answers to those questions here:
Additional information may be obtained from the documents noted here:
Lone Wolf Terrorism – A Brief Bibliography.
Increased gun control will have an effect on law abiding gun owners.
As goes gun control, I happen to be among the crowd that thinks that nationally established/enforced dramatic curtailments in the availability of guns and ammunition will reduce the incidence of gun-related acts of violence and death. IMO, Mateen was highly unlikely to have been able to kill some 50 folks using a bow and arrow, throwing knives, a baseball bat, etc.
Among the major lines of argument gun rights advocates offer is that guns contribute to one's greater personal safety, presumably by either increasing the risk a violent offender faces to carry out their deed(s) and by enabling non law enforcement/non security personnel to intervene in situations like "Pulse" and the other mass killing events you noted in the OP. Well, if that's so, why in OK, VA, TX, and CO, each a "gun friendly" state, did no lay gun owner intervene to effect an end to the violence before the cops did?
Hell, three of the mass shootings were in TX, one in
Killeen, TX, a place that has no paucity of gun shops, indeed two are custom gun making shops, and an army base, Ft. Hood. That in a town of ~135K people, of whom nearly 60K are Ft. Hood employees, which is to say, if the Army isn't the reason one is there, demographically, there is a very high likelihood that one is "rural" in one's outlook, and, IMO, "rural" folks love, own, and carry guns. Where were all those gun toting Texans when
Lubby's was "shot up?"
I may be mistaken, but to date, I'm not aware of so much as one incident where gun carrying civilians have acted to stop a terrorist. So, what is the point of having all these armed citizens when they are clearly ineffective in helping to prevent a damn thing or in dissuading terrorists from attempting to carry out deeds like "Lubby's" and "Pulse?"