I'm not an expert on patetnts, but that seems backwards to me. If I get a patent for something, someone else can make a trivial change they call an improvement,

I'm not an expert on patetnts, but that seems backwards to me. If I get a patent for something, someone else can make a trivial change they call an improvement, admit their work is derivative, and get a patent for that without any cooperation or licensing from me? And then if I iterate and get sued, even though I can show I hold the original patent it's not a slam dunk win for me in court?