The ML stereo is very dependent on equaliser settings, balance and the source. In my old RX I kept it one towards the front and the equaliser from memory was set to +1 treble, +2 mid and +2 as well.
Worth remembering that it doesn't sound good at all when streaming. Ideally you need it on a CD or USB drive. Additionally, the volume needs to be set pretty high, otherwise the details aren't present.
Salesman is talking BS - the F-Sport has stiffer suspension to begin with. The Premier is designed to be the luxurious one in the range with a smooth ride, hence the trade off is cornering wallow! F-Sport is stiffer and almost completely reduces wallowing in the corners. TBH I find the Sport+ mode in the 4RX too stiff for normal driving, it skips across every expansion joint so I tend to use Sport mode instead when I feel like it.
This is the main reason the F-Sport with Premier Pack was brought out - to allow customers to have all the options of Premier with the more dynamic drive
Additionally, if you don't really need the 360 degree camera of the Premier, just go for an F-Sport with HUD/ML/Pan roof and save some money - although it appears the F-Sport has better residuals so you may not save much