Tend to use a Givi tank lock bag for day to day stuff and day ride outs. Give V47 topbox if I commute to take work bag, sarnies etc.
OE panniers only for a short holiday/tour and panniers and top box for longer/two up tours, and in both instances Give tank bag to hold wallet, phone, camera, glasses etc.
As I mentioned in a thread a while ago, for an example, my son and I did the motogp at Le Mans last year, all three pieces of hard luggage full up, combined weight of me and him and luggage around 230kg. At up to sensible cruising speeds around 80mph no problems, top speed dropped to an indicated 105, (fo r the interests of science).
I think it is all a matter of what is your preference and how you use the bike, all the hard luggage is easily removed and stored in the garage when not in use and takes a couple of minutes to remove/add so is hardly a chore.
Oh and in a ride of two hours in heavy rain last September in the Ardennes, the OE panniers/topbox were watertight.