I was playing Orbiter long before KSP came along. It taught me all I know about orbital mechanics. It helped ease the learning curve in KSP a lot. But after KSP came along I completely lost interest. KSP is a lot more fun and there’s a lot more to do.
Still had a laugh when my friend who made fun of me for playing orbiter ended up buying KSP, getting frustrated, rage quit and asked for a refund.