I agree with this assessment — it seems pretty clear that Voyager writers just expanded on how quantum slipstream works as they tested it. In the second episode it appears, Starfleet fine tuned it — like discovering Warp 1 then figuring out how to go Warp 9 — but I doubt VOY invented two entirely different versions of it with radically different designs (which wouldn’t make a whole lot of sense.) Otherwise, that would be like assuming any new warp drive doesn’t use dilithium unless they specifically state so in the episode.
Here's the thing... VOY crew DID in fact come up with a radically different design.
The v1 of the QS drive had several differences vs the v2 as seen in Timeless.
v1 QS properties:
Top speed = 300 Ly's per hour (this probably cannot be sustained indefinitely, but by shorter periods even by the fake Dauntless - I'd imagine anywhere between 12 hrs to a day - possibly more because the fake Dauntless was specifically designed for Slipstream).
Sustainable long term cruising speed = 666.666 Ly's per day (to traverse 60 000 Ly's in 3 months).
On VOY, v1 produced quantum stresses on the hull which prevented Voyager itself from being longer than 1 hour in Slipstream.
No mention of Benemite Crystals for v1.
v2 QS properties:
Redesigned to include Borg Technology, Benemite crystals and quantum matrix.
Top speed = 10 000 Ly's per minute (judging by what we saw in 'Timeless' because troubles didn't start happening until 17 seconds into the flight per the dialogue - after that, there is no more than 45 seconds or so before future Kim managed to to shut down the drive).
In this version, the quantum stresses weren't a problem, but as it turned out, VOY's computer couldn't calculate the phase changes of the Slipstream threshold as it was forming - which effectively lead to its icy demise in an alternate timeline.
At any rate, benemite crystals are a crucial part of V2 QS drive... probably because it also includes more alien technology in the mix and is a more refined version vs the first one (like someone else mentioned, an equivalent of jumping from Warp 1 to Warp 9 in months).
The v1 was never stated it needed benemite crystals... and simple modifications on VOY at the time were enough to make the technology viable for VOY (apart from the Quantum Stresses).
At any rate, I still maintain SF could have made use of V1 without the Benemite Crystals to replace the Warp drive for fast travel times.