I'll give the devil his due, 20,000,000 Glocks world wide is a VERY good indication of a successful HG platform. And lets not forget Glock magazines are the industry standard for problem free reliability.
Beyond all debate while Glock was NOT the first to produce a polymer framed HG that title belongs to H&K, Glock was the most successful at first producing then secondly marketing a very affordable extremely reliable, high capacity, with only 34 parts a very economical to mass produce semi-automatic HG.
Only reason I do not own a Glock and I like Glocks just fine is because Glocks do not like me. Or more accurately stated the grip ergonomics of the Glock do not like me. Can I shoot one well enough to defend myself? absolutely. But if I am spending my own money I am going to buy a gun that meshes as well with me as I can find and that is not a Glock, nor is that a CZ P10c for that matter.
My two Walther PDP's and now three M&P Shields are the equal of Glock in reliability, if anything are more inherently accurate and unlike the Glocks' ergonomics that for lack of a better way to express it wants to constantly argue with me, my PDPs and Shields seam to melt into my hands and wish to eagerly cooperate when I shoot them.
Glocks are a great gun and have been copied by EVERYBODY but S&W and Walter's version of the Glock are in my opinion better from an ergonomics stand point and if one has a choice one tends to buy what works best with them VS what does not.
Glocks are a great gun, it's just now there are a very large number of other polymer framed guns that are unquestionably the equal to Glock in reliability and price point.