Tube sealant vs. tire liners vs. puncture-resistant tires -- which best prevents flats? Clarification:

I am not asking for a solution to punctures, or about the nuances of ride quality with the various solutions. I am asking whether one method of reducing punctures has been proven better than others through scientific testing. 

Preface:

I often see people online using tubes with sealant rather than tire liners or puncture resistant tires, and wonder "why?" The slime is messy, can clog the valve, weighs more than liners, and does nothing to actually prevent a puncture, but rather waits until the puncture occurs to go into action filling it and (hopefully) coagulating in the hole. I've read that this really only works on small holes, too.

Purely anecdotal evidence:

I've ridden for the last eight years on the same route during my commute. I started with tire liners on regular tires, then went with Continental Gatorskins (Kevlar belted), and am now on my second set of Vittoria Randonneurs (double-shielded), and of the three setups, only ever had punctures on the Conti's -- at least two flats per year (grrr!). Zero flats on the Randos in nearly four years while laughing my way through the fields of glass.  I see Schwalbe Marathons recommended more than any other brand, and while many say they've never had a flat with them, I also see some cyclists posting that they've had flats with those, too.

It just seems to me that there's no competition: double-shielding wins, IMO.  It's less hassle that liners or sealant, and just as protective as liners/more protective than sealant, and generally weigh the same or less than sealant-filled tubes or tire-liners.  Not to mention the cost factor over time.

Question: 

Can someone explain the advantages of using liners or sealant over puncture-resistant tires, specifically relating to resisting punctures?  Have any scientific studies been done to compare the three methods?
There is more to tire set-up than just puncture proof.  Many are also interested in tire suppleness, traction and rolling resistance. Tubeless tires are the in thing at the moment because tubeless construction take material away (aka the the tube) and allows lower pressures, which results in a more supple tire, that has more traction and often less rolling resistance.  

Supple tires can often roll faster and with less effort as they deform more easily to surface imperfections. This translates into a smoother ride and less pedaling effort and more traction. Many of the puncture proof setups add material to the tire making the tire carcass stiffer, this in turns means it takes more energy to deform the tire when rolling (or encountering a bump), which in turns results in a harsher ride and a higher rolling resistance (the energy to deform the tire has to come from somewhere; i.e., forward momentum).

Summarizing:


Tire Liner - Cheap and reusable as it can be applied to current tires, but has a fiddly set up (e.g., getting the liner to stay in place), will reduce suppleness of the tire and does not provide puncture protection on the side wall.
Puncture resistant tires - These have what is in essence a liner built into the tire carcass. Because of the unified construction should be more supple build than a tire liner and vary the degree of coverage. Different manufacturers and models will have different trade-off between suppleness and puncture resistance.
Tubeless - Primary goal is really to create a lighter, more supple tire, that can be run at lower pressures, the setup also happens to have good puncture resistance properties if sealant levels are maintained. Mounting a tubeless setup can be a hassle (i.e., you need high pressure to seat the tire), sealant is required and handles sealing the system including handling punctures. Sealant also needs to be topped up every few months as it dries out, and without sealant you lose puncture protection. The setup also requires wheels with tubeless compatible or tubeless ready rims, tubeless tape, and tubeless valves are also required. The design goal was less to be "better" than (1) or (2) in terms of puncture protection, but optimizing the tire for a different set of criteria (i.e., weight, suppleness, traction, rolling resistance and puncture protection).


If puncture resistance is your only concern then your "double-shield" setup looks like a good solution and will be easier than tubeless.