I never took that message as an indication that i will have to slow down, but a notification that i'm being slowed down
After nearly 10 years of a confusing message I am not suprised you inferred that meaning to it. Always seemed like a command or at least a suggestion to me, which I then couldn't act upon in most instances, which was always frustrating.
IMO, if they had kept the slow down message they should have at least made it pop up while you could still actually act upon it, instead of when its already too late. Now they've changed it to gravity well, this obviously isn't necessary. It comes across as a notification that you've made a mistake rather than a misleading suggestion that action can still be taken.
An appreciated change, one of the more significant ones to me as a player along with the fact they've fixed that annoying shadow bug that completely destroyed immersion especially when landed on planets.