Dunno about that...
I've cut some rather nice curves with the rotary blades. The biggest problems with rotary cutters are the need for a cutting mat and if the ruler slips, the straight line goes out the window.
The need for a huge cutting mat and the cost of replacing blades - even if you do sharpen them they don't last that long.
Stand over the ruler and press down; it doesn't slip if you do it properly.
I'm with
@Ohsewsimple in using the rotary cutter for bias tape or straps but I still maintain that scissors are more accurate for cutting out - look at some old GBSB programs and you'll see some really inaccurate cutting out by contestants who used rotary cutters. I recall one who must have sliced at least a quarter inch off the pattern edge, and thus also the fabric.