ITAR regulations restrict GPS for civilian use to a maximum altitude and maximum velocity, but this is solely a software limitation that is increasingly becoming less relevant.
Although selective availability has been disabled for a very long time, even before SA was turned off it was easily possible to get a precision measurement by integrating over time as the SA error was pseudo-random. It is also possible to use things like the phase information from the non-civilian 'encrypted' signals to increase accuracy even though the data cannot be decoded. Some survey-grade receivers were doing this even before SA was disabled, and it's pretty standard now in the precision GPS world.
Your understanding of GPS is quite out of date. GPS began adding a second L2C frequency for consumer use 15 years ago, and started ramping it in 2014. They are in fact in the process of adding a third civilian signal called L5. You can get accuracy from the consumer signals Galileo is great, but I wouldn't be holding it up as a crown jewel of GNSS. They have had some major missteps and operational issues in the recent past.
For consumer applications, multi-GNSS receivers are really where it's at. Combining GPS + GLONASS + Galileo + BaiDou is not simply an excercise of comparing the resultant positions given by each networ, but actually being able to combine the information to produce a single faster or more reliable measurement. For instance, getting a 3d position from 2 GPS satellites + 2 Galileo satellites when ordinarily you would not even be able to get a 2d position from either network in that situation.