Operating Vs. Static Locomotives

I was reading the RGS 20 threads and got to thinking about the debate between replacing original fabric to mke a locomotive operational versus leaving a loco original and not operating it. However I think there is one fact that is often neglected when making the argument about leaving a locomotive in its "original" condition.

Most of the locomotives that are in their "original" condition are sitting outside on static display. That very action is causing the engine to lose original fabric. Every year the weather turns X number of pounds of metal into rust, and after 40 years of outdoor display you have lost the equivalent amount of metal that no. 20 lost when its boiler course was replaced.

So the only way for this argument to be valid is if a locomotive is stored indoors and deterioration is halted. Otherwise its a false argument and we shouldn't waste time discussing it. Most of the static locomotives that I see in outdoor display look NOTHING like they looked when in service.

If RGS 20 was not being rebuilt for service where would it be sitting right now? Would it be sitting outside? Would it appear as it did when last in service, or would it have umpteen layers of black paint covering cancerous rust, with non prototypical "do not climb" signs hanging from its steps? Is that really preservation??? Park an operational steamer next to one that hasn't operated in 50 years and sits outside and lets see which one more closely resembles the appearance of a steam locomotive during its service life.