A perk tag is only a soft limit, unlike the ENY limit. If you got the points you can fly them and you fly them for free as long as you land. Players that spend most of their time in planes with ENY higher than 5, very quickly rack up hundreds and even thousands of perk points. If you fly for the less populated countries you earn more perks and get a discount in the perk tags, making some perked rides dirty cheap.
The perk tag is mostly a psychological limit. With just a couple of hundred perks one can probably fly nothing but Chogs for many tours, even if his K/D is unimpressive.
btw, I too noticed an increase in the frequency of 190s and 109s that I meet. Not that it bothers me, they go down and/or kill me just like that P51s and Spits do. Also since I tend to fly mostly allied planes, blasting the Luftwaffe out of the sky seems more appropriate. Maybe it is just the player population that matures - new players gravitate towards the Spits and P51s, but as players get more proficient, many discover the crisp handling and firepower of the 190 and the excellent balance between speed, excess power and turn of the 109s and switch to those planes. I rarely notice two-weekers these days, so either I am getting blind to them or that there are just few of them and the rest of the player base are more experienced on average.