65-30 would be unusual. I've seen it scrub 10-15mph at highway speeds (e.g. 60+ mph), more akin to you suddenly lifting off the accelerator. It feels more severe because you're not anticipating it (same reason passengers tend to be more susceptible to getting car sick while you're fine as a driver). It'll happen every once in a while, but having the right mindset here and knowing it could happen helps. Tapping the accelerator will get you back again.
Most would say on the highway it's pretty solid, even when it goes down to sudden pockets of stop/go traffic. And once you're in that stop/go traffic, there is nothing better. It'll creep along and stop as traffic moves, although some say it's a bit aggressive accelerating/stopping. Switching to Chill mode helps if it really bugs you.
On local roads (without FSD beta) it's average ... not really designed for it and not really recommended even though you can do it.
It's probably in its worst form in FSD Beta - but being a work in progress, it is unpredictable as you'd expect. It's frustrating at times, and rewarding at other times.
In the end, not worrisome. It's a damn good system, but it's constantly being developed so behaviors will change over time. People tend to get excited by software updates because some of them do improve the car's autopilot behaviors.