It’s all a compromise.
Start with the basics. Recognise that, as you are sitting outside and shoving yourself through the air, sometimes you are going to be hot / cold / wet / dry occaisionaly in the space of a few hours.
Try not to fall off. It usually hurts, irrespective of what you are wearing.
Accept that you might fall off, then work out whether you care what damage you may or may not do to yourself. Of course, if you hit the side of an articulated truck whilst ‘making progress’ it may not make much difference whether you are in a kilt or a suite of armour.
Leather. Strong. Good abrasive properties. Lots of styles and colours. Natural. Breathes well but only up to a point. Gets hot when it’s sunny, hence ventilation holes punched all over the place on some kit. Not renowned for its insulation properties (especialy when there are holes punched all over it), so fresh in winter. Not very waterproof. If worried about wet, buy oversuite and maybe worry about sweating. If worried about cold, wear a vest.
Non-leather. Man-made fabrics. Man, because he has evolved above the ape creatures of the isthmus, can engineer out some of the faults in God’s handiwork but cannot fix others without some compromises. Works reasonably well, hot or cold. Can be made totally 100% waterproof in up to monsoon like conditions but this may create breathing problems (no point stopping water getting in if it can’t get out). Having some method of getting the garment on and off, whilst catering for dangly appendages called arms and legs, and having a zip for the fifth appendage, creates its own little challenges. In order to overcome the challenges the clever folk mix and match fabrics, some to keep you warm / cool, some to keep you dry and some to help prevent you ripping too much skin off. Some that can be sown or welded together and some that can be reasonably easily shaped to even fit the fuller figure of the average GSer. Yes, most will melt if you get them hot enough and may even burn you if you generate enough friction but so will the seatbelt in your car. However, it may be worthwhile trading-off a burn to quite a small area, to stay reasonably warm / cool and dry most of the time, compared with boiled, freezing or wet or with road scars that start prevent you from flopping down on your a*rse for several months?
None of the above will stop you breaking your leg however, or turn you into V Rossi or M Coma.
It’s your body, wear whatever you like.