Gustavo
I would recommend switching Designers as soon as you level up. I don't have the rates of next season Design Point gain for lower level CDs, but when they are 1 level lower, they give less points.
Take the example of level 20 accounts, they need lvl 20 Designers or lvl 19 5 stars.
Even if the star rating is the same? OK cool, I've already got a level 18 4.5 star CD in place, I was just curious. It's so hard to find available CDs with the desired strengths and weaknesses when you're up at this level