That's the truth, everything else is just rose-tinted nostalgia. Grabber II, Ripper II and the G-3 Tribute are all better-made than their ancestors and sound rounder, more consistent and more assertive too.
Aside from the build quality item (which I am skeptical about given the amount of fit/finish complaints on new Gibsons we see around here, but I can't speak to personally.... the few vintage Rippers/Grabbers/G3s I have seen were damn solid, though I suppose 40 years of use can hide finish imperfections), isn't any judgement about the sound completely subjective?
I mean, I love vintage mud. The new SG bass sounds great, but my vintage EB3 does a thing I really like that the SG can't. Yes the SG is more versatile and sounds 'better' in a typical this-is-how-we-bass way, but when you have multiple instruments, I would think that a certain specialization is actually more useful than having a bunch of jack of all trades, and I don't particularly care to sound like anybody (everybody) else anyway (I go to great lengths not to). Since the pups are so different on these updated G-series models (not reissues, given the "II" moniker - I appreciate them making this distinction) this may very well be an improvement in many ways (technically; on paper etc), but those old ripper pups (mini-muds as they were sidewinders) had their own special thing, which some people may legitimately prefer, as did the original (Bill Lawrence) G3 pups (I really love those, the new ones may be very good too, I haven't tried them yet). To chalk it up to pure nostalgia is not entirely fair. Though I understand their decision (being different has not served Gibson so well in the bass market historically), I do think that Gibson is missing an opportunity here by letting these old pup designs languish unused (could they not be updated and improoved with modern materials and manufacturing but still retain a basic character and advantages of the original vs a completely differant design?). There is a market for them as clearly shown by consistently rising ebay prices on vintage units as well as clone reissues by other makers. Gibson has been one of the most innovative companies as regards bass pups and it's a shame that they are abandoning much of that heritage to try to be more Fender/Musicmanish (this is, paradoxically, also something that has historically not always worked out for them so well).
Also, I find that 'round' and 'assertive' are, if not quite mutually exclusive descriptors, not exactly things that are easily reconciled in my mind, so your description is a little confusing. To me, round means mellow in a sine wavey way, with good bass response and extension, while assertive conjures thoughts of mid-forwardness, maybe even a little aggressive brightness or clank. I have a hard time imagining a sound that is both of these things. .. but that's the eternal problem with descriptions of tone.