My assumption is that all intelligence services in all countries would love to have access to fully compromised networks. They spend all their time thinking about how to access information, so they would be fairly incompetent not to consider this.

Does that mean that all systems are compromised? No, because there are risks associated with tapping in to these systems. Partly it depends on if they have access to the systems, but mostly on the possible blow-back if they get caught.

Example: Swedens FRA (NSA equivalent) could in theory ask Ericsson (a Swedish company), to install a backdoor. But, Sweden has a fairly free press, and there are good chances that someone would leak this information. If it got leaked it would be a major scandal that could go as far as toppling the government and destroy one of Swedens most important export companies. Its very risky, and its a risk no one wants to take, so the parts made in sweden are probably not compromised.

China, on the other hand has almost no risks associated with adding backdoor. No free press, hard suppression of whistle blowers, and since most foreign intelligence services already assume the equipment is compromised, there is no real reputational damage either. I assume they are all compromised, why wouldn't they be?

The US is somewhere in between.

Sometimes companies are compromised by intelligence services, but much more often I think its employees. Why try to change Tim Cooks stance on privacy, when all you need to do is find one Apple employee, willing to take a sack of money to "do their country a great service"?