How to properly multiclass?

So... thinking about multiclassingo on Runesia, and figured that I dont know how to do it.

Suppose I want a Bard / Witch

If I level her up as a Bard first, getting her to the highest Bard class and getting 5 proeficiency, she is already at lv 25.

If I switch her over, she will level her last few levels with the stat gain of the lowest witch class? Feels like there is another way to do this efficiently that I am not seeing, because I really dont want to loose those best stat gains possible....

Whatam i missing?