I believe devs recently changed the entire graphics engine of the arrange, to make it also compatible with the new OSX system (which I believe it is hardware accelerated?) and it is much faster with many hundreds of tracks than before. Justin said it would probably break many things, but that didn't stop him to do it.
I really wouldn't complain if we could have GPU accelerated graphics on scripts. Some scripts can become heavy on graphics. And when I scroll the arrange for example, they can stop to be refreshed creating some problems as I described here:
https://forum.cockos.com/showthread.php?t=163905