Not having the skill level effect active but being able to grind it makes me think it will possibly lead to many bugs that can be exploited at least in the beginning. Imagine getting skill gains at 80 lvl as if your skill was 20 lvl.
Another possible exploit could be that you would get max skillgain from imping a 30ishql item having 20 active skill while actually having 80. so you dont need a 90ql lump to grind your skill on that chain armor piece cuz it is about 30ql.
Slower rate makes it balanced provided there are no exploits available. How much slower tho? Not slow enough and you will have people running many free chars on their strong computers to grind them up and sell them. Too slow and it has very little purpose.
Does it make sense for a genuine newbie to grind up to 90 at weaponsmithing while freemium all the time? Not really. So wouldn't it be better if it was limited at 40 or 50. You have 20 effective but you can at max get 50 inactive skill unless you prem up. It will be on a slower rate, but not too slow.
Another good option in my opinion is letting freemiums have full rights (can grind them and use them at current lvl) to few certain skills to a certain level like 40-50. Botanizing, Forage, Digging, Stone Cutting, Farming, Carpentry seem like good candidates to me.