I would say that from an European POV, USA's democracy has been compromised way earlier than Turkey's. While Erdogan is somehow a new element in Turkey's democracy, systemic corruption in the USA has been prevalent for almost a century, while Turkey had a somehow solid democracy in place.

Trump is just an error in the system, a person that is incapable of following the rituals and gain advantage of a low-profile attitude.

"Turkey had a somehow solid democracy in place."

The civic quality of the Turkish system has quite a troubled history. Turkey's government has been held at a gunpoint by it's military for decades:

https://en.wikipedia.org/wiki/Turkish_coup_d%27%C3%A9tat

"systemic corruption in the USA has been prevalent for almost a century"

I think that needs a quotation. US history is filled with genocide, empire building and after the 1970's, funnelling the profits from the economy from the employees to the capital owners. That, however, is not the same thing as corruption.

We're not discussing who is 'good' or 'bad', but comparing the quality and nature of institutions on the national level.

AIUI the Turkish military acts as a safety valve when the government gets more Authoritarian/Islamic; the military step in and a democratic, secular status quo is returned. Is that not the case?

Certainly the couple of military coups there I know of seemed to rapidly result in establishing a strongly democratic constitution and a group of representatives to whom the assumed power could be handed over to.