They actually stepped up their game dramatically about 2 decades ago or so, and nothing in "quality" improved or changed since then, since it was already matching that of the best in the industry by that point. The irony with your point about baggage, which yes likely is one other benefit to the name change, is that people are now seeing these as newly improved instruments with open minds and realizing how great they are, when in fact they were making the exact same instruments for at least 20 years if not longer in some cases.
So, to speak of facts and evidence, what sort of stuff did you dislike in the quality of "carvin" branded keisel instruments that has changed in the same "keisel" branded instruments?
I would venture to guess the tone - as their much older bass pickups, and older yet preamps, tended to be pretty upper mid heavy much of the time, which wasn't everyone's idea of a great bass tone. That was when "buy a carvin, replace the electronics" became a common recommendation to get the best instrument and then electronics to match.
However, for myself, I can start by saying the woods have always been super high quality in every Carvin I've played. Electronics were great for the past 15 years (when the icon came out) - (the 99 series pickups are excellent and newer pickups are even more interesting), preamps on my icons are equal to the best stock preamps I've ever used, again a 15 year old design. Fit and finish is tied with the best built instruments I've ever owned (Alembic and Warwick). Fretwork is literally textbook perfect on every Carvin I've ever played. Bridges are excellent designs with immense flexibility yet rock solid stability.
Personally I'm not basing this on memory, I'm basing it on having a Carvin bass here beside me (see it's in my profile pic, fretless icon 5). The Keisel Icon 5 fretted bass I borrowed was months ago, but recent enough to realize it was EXACTLY the same instrument. Having borrowed it, I now understand that there is no reason to ever sell my Carvin, there's nothing to be improved upon.
I DO like the newer models though, specially some of the headless ones.