Your Kershaw Leek blade thickness is 0.090". This is fine for easy-going EDC. It slices well but isn't strong enough for any considerable prying or side pressure, as you have found out. But it's instructive.
A thicker blade will be stronger, all other factors being equal. Please note that many, many EDC knives out there are 3mm or approx 0.125" thick. Knives that are meant for heavier duty are often 0.140"-0.160" thick. The famous Chris Reeve Sebenza (both small and large models) is 0.125"; their Umnumzaan (Boss) model is 0.140". Their newest model, the CRK model 25 Sebenza, has a blade thickness of 0.140".
The BenchMade Adamas blade-steel is 0.160 thick of D2 which likely trumps the Spyderco Gayle Bradley's 3mm of CPM-M4. Given that the Adamas blade is 33% thicker blade-stock than the GB, which do you figure is tougher? And my ZT 0550, known for heavy-duty applications, with blade-steel of 0.156" of S35VN, is right there alongside the Adamas for toughness.
The rather popular DPX HEST 2.0 sports a D2 blade that's 0.187 thick, titanium framelock, Lion Steel Rotoblock. Tough little honey, and TWICE the blade thickness of your Leek.
Blade thickness can be easily overdone, and just makes a good knife heavier than necessary for casual EDC, and often ensures that the knife is a poor slicer. Many times, a thick-bladed, heavy-duty knife will be left home as it is too heavy to be carried with comfort. Before you buy your next knife, check with the manufacturer's website or Google to determine (at least) the thickness of the next blade, as it oftens tells you how heavy-duty the design is.
Certainly, the "grind" of the blade, blade-shape, the blade-steel type and heat-treating, spine narrowing as you approach the tip, is also important, but here we are just dealing with generalities of blade thickness as one parameter.
Sonnydaze