I doubt that without removing and inspecting and even flowing any fuel injector most people would not be able to tell as the fuel injector starts to degrade in it performance. So most often the "no issue" commits only mean you don't know!
Frequently while ECU calibrating and looking at DATA logs I always see a cylinder that just wont get exactly up to the rest of them. While no DTC are generated pulling the fuel injector and replacing it with a new one cures the problem. I won't calibrate for performance use any customers ECU without a clean bill of health from one of several Fuel injector rebuilding companies or that they have replaced their fuel injectors within 10k miles or less.
In the fuel injector by not using the best gasoline or as we say top tier which I recommend that to be 2 Chevron and Shell, than Union 76 ,Exxon and last Texaco or if I can contact the supplier and get the formula used or ingredients' then you are not getting what I would call the best and "NEWAGE" gasoline. Don't fool yourself not all gasoline is the best at keeping your engine running the best and keeping parts like fuel pumps and fuel injectors clean.
Using poor quality fuels slowly effect the Needle, seat guide and the pintle operation in the fuel injectors. As a varnish slowly form the ECU does not detect the drop in performance until the varnish is so bad that the fuel injector can not pass fuel properly and that changes the air fuel mixture that the ECU compensates for until it becomes so bad that you finally get a DTC. The first time a DTC because of a Fuel injector many will replace other suspected parts while clearly the DTC. When the DTC returns after a short time DIY again start replacing more parts and may even finally replace on or all the fuel injector that finally cures the returning DTC. All this time most will say they have no drivability concerns. IMHO most of this was caused from not using a top tier gasoline or at least occasionally using some bottle fuel system additive/cleaners.
BTW even OEM fuel injectors like MAZDA oem injectors new are seldom balanced and often not all the same performance . On a street driven vehicle it may not be practical and so few actually would even consider it but by having your fuel injectors cleaned and matched you can increase your power output of the engine. Its only a small amount but all those small amounts add up. You would see a slight improvement in MPG is you simply had your fuel injector completely cleaned at about 30-60k miles.
The place I use, we use in the shop and I recommend for performance is RC Injector service.
Most any fuel injector service company can support everything I posted in this response and many even have actual Dyno Data and or ECU data logging as well before and after serviced fuel injector flow ratings
On my own personal Mazda I do a fuel injection cleaning every 10,000 miles my own equipment in my DIY home (not the shop lol) garage. . It takes me about 1.5 hours.