Ahoy and welcome back aboard!
Yes - the closer you get to 700(+) total skill points it seems to be harder/take longer to gain. Also the closer you get to the skill cap for any given skill the gains get harder/come slower. Some players have a character that they use only for training and then use soulstones to transfer the skill to another character.
I am sure there are formulas and sticky posts with more detailed information.
Good luck!