Have you tried tweaking the advanced support generation settings? You can try turning down the Density.
And when you’re in manual edit mode you can draw a selection box around a bunch of touchpoints and delete them all at once.
As for other slicers… I’ve used Formware in the past for complex support structures where I needed more control over the geometry of my supports. Here’s an example. It wasn’t faster than Preform but beat modeling them in my CAD tool. I encountered some bugs but the developer was pretty responsive.
I have noticed Preform get pretty bogged down with larger models intended for my 3L. The performance of the software feels like it’s degraded somewhat over the years as more bloat features are introduced. Turning off the Printability toggle while you’re editing helps a lot (of course you need to turn it back on now and then to evaluate the results).