Strange question, and certainly not one i'd considered before.
I'd argue that a typical base layer is going to do little/nothing to spread the load, and the correct course of action if you feel the straps are uncomfortable is to either try a different brand of shorts or a size bigger.
Personally i go up a size in Castelli shorts for exactly this reason. I'm ...
Three things come straight to mind.
Pockets - there is no storage in bibs, other than a small pocket in the back intended for a race radio only, and this is just on high-end race-specific items
UCI rules - I bet there are some written rules around jerseys, sponsor's logos, and skin suits that will have an effect on what can be worn, and when.
A sponsor ...
Reasons not to:
you block access to your jersey pockets
it won't be doing much to spread the load
If your bib is so uncomfortable that you think you need something to pad it with, you need a correct size bib.
if they ARE correct size and the straps are still cutting into you, you're wearing them WAY too low. Pull up. You need to jam them right up there
I live in a tropical country, so most of the year the temperature is above 20° Celsius, so coldness is not an issue here. It can also be unpredictable for rain.
I have tried both strategies: a) (try to) keep dry while riding under the rain and b) (act like) not caring about it.
With strategy a, the problem is sweat accumulates inside rainproof gear, so I end ...