"Prior to deregulation, airline service was barely a skeleton of what we see today...", you stated. I disagree. Using my home airport as an example, prior to deregulation, we had L-1011 service to the West Coast: LAX-DAY-IND-LAX. More non-stop flights on planes, including jets, that were larger and more comfortable than the regional jets of today. An AA non-stop 727 flight to LGA with a good dinner(!) in Coach. We were a hub airport with many non-stop choices for Piedmont Airlines including flights to/from Boston with meal service in Coach.
This is exactly why service changed. Putting in large airports into small cities and serving hot meals to every passenger is just not sustainable anymore. DAY is not big enough to sustain a hub anymore either. That said, the regional jets of today are more comfortable than they were. I see only a couple of flights on the CRJ-200 (50 seater) but quite a bit of service on the larger 70-76 seaters that offer 1st class, extra legroom, etc with either buy on board meals and some meals for first class for the longer flights. That ERJ-175 is a pretty nice ride and I prefer that to most Airbus and 737's even. All those services are still available if you don't mind paying for them. Probably similar to the amount you payed during regulation.
DAY has not quite a skeleton service, yet. But, if the reduction/elimination of TSA security check points take place as has been proposed very recently, our air service will be negatively affected, in my opinion. Only Delta is flying larger jets and that is only on the DAY-ATL itinerary. Deregulation has promoted the rise of the budget airlines and lowered the fares so that flying is now like traveling by bus was when I was in college. But, even airports such as DAY have suffered the loss of some of these budget airlines. You may disagree with this statement if you wish. But, my hometown airport is very much under served given the tax payer's money that has been spent in building and maintaining and improving our airport.
I don't think the TSA cuts are going to happen at all, but even if they did, I doubt DAY would lose the TSA, since most of the flights there are on jets larger than 60 passengers seats.
Looking at DAY passenger totals, they have indeed lost passenger in recent years. A peak of 1.4 million in 2010 down to a measly 950,000 in 2017. It's hard to say why, but my guess is that CVG has grown quite a bit since Delta shrunk it's hub and now LCC's have finally entered the CVG market. Perhaps CVG is stealing your passengers. Back when Delta had the huge hub, they increased prices so much that people would buy a ticket on Delta from DAY and just make the drive there and then connect right back through CVG again. On the way home, they'd just skip the last flight back to DAY.
Part of the problem with deregulation, is the constant merging of carrier's, and consequently the closing of many hubs, or reducing service drastically. Look at what happened to St. Louis, Pittsburgh, Raleigh, Nashville, Las Vegas, Reno, etc....all just from AA merger's and acquisition's....add to them the other hubs suffering from similar on DL, and UA....
Nashville is the 4th fastest growing airport in the US right now. It has added British Airway recently. Raleigh is now a mini-Delta hub with a flight to Paris. AA still has a flight to London. RDU has carried more passengers now than ever at 11.6 million in 2017. Pittsburgh did add British Airways as well.