The SLS option would have entailed a direct trajectory to Jupiter taking less than three years. ... The move to Falcon Heavy saved an estimated US$2 billion in launch costs alone. NASA was not sure an SLS would be available for the mission since the Artemis program would use SLS rockets extensively, and the SLS's use of solid rocket boosters (SRBs) generates more vibrations in the payload than a launcher that does not use SRBs.
Fun side fact, solar flares and solar wind have to be taken into account during satellite orbit calculations. During one of the large flares earlier this year, the solar pressure pushed many satellites at least a few km off their orbits. Sats facing the sun lost altitude from the increased drag pressure
On the opposite end of the spectrum, New Horizons was only 478 kg [1] and still holds the record for the fastest thing ever launched from Earth. It also did a gravity assist flyby around Jupiter and it still took 9 years to get to Pluto.
To expand on this a bit, it's the fastest launch. The unqualified speed record goes to the Parker Solar Probe in 2018, and was previous held by Helios B way back in 1976.
The distinction here is that New Horizons has spent it's life traveling away from the Sun, and it costs energy and thus speed to do so. Meanwhile, solar probes gain speed during their fall towards the Sun.
