Given a selection of 100% solid epoxies, are they all equal? No. No more than a 2 seater smart fortwo is equal to an 2 seater Corvette Z06.
Epoxies are all different. They may share some of the same basic ingredients, but there are many other ingredients that make a huge difference in the performance of the final coating, and even a difference in how easy they are to apply.
For example, our recommended system for most DIY projects has two different epoxies, BondTite 1101 and LiquaTile 1184. Both are 100% two part epoxies, both have a 2:1 mix ratio, but both are very different and do different jobs. They have at least a dozen different ingredients, many of them unique to just that particular epoxy, and of the few ingredients they do share, they are in differing proportions. And that's just for two 100% solids epoxies from one manufacturer!
The LiquaTile has ceramic content, which most epoxies don't have (quality ceramic ingredients are expensive). Ceramics gives it better abrasion resistance and strength in addition to its ability to absorb shock from falling items (unlike ceramic tile). And then even other high end epoxies that do contain ceramic content don’t necessarily have the same quality ceramics that LiquaTile has. And if they do contain those premium ceramics, it may not be formulated the way that WCC epoxies are. The ceramic content of LiquaTile is linked together, so essentially you have chemical chains of ceramics binding the epoxy together. That makes for an extremely durable and long lasting floor coating.
So again... No. Epoxies are not equal, not in content, not in application, not in performance, not in durability.
As for recommended thickness, it's best to follow the manufacturers' guidelines. In our case for most home and shop applications we recommend a 3 coat system for maximum durability and lasting appearance. Generally the total dry coat thickness would be a minimum of 22 mils, which would be 5 mils of primer coat, 12 mils of body coat, and a clear coat of 5 mils. The primer coat would be our BondTite 1101, a 100% solids epoxy with extremely tenacious grip strength. That would be followed with a coat of LiquaTile 1184, this pigmented epoxy will give your floor the ability to withstand shock and impacts, protecting the concrete. Finally a 5 mil clear coat of BondTite 1101 to help resist abrasion and give your floor that high gloss finish. Our epoxies are 100% solids, there is no water or solvents to evaporate, so what you buy and what you apply is what you benefit from 100% when it cures.