How to make a true comparison?

In reading another post asking for observations between two turntables, a rather obvious question occurred to me - what is the best way to make a true comparison?

Solution 1 would be to use the same platform, mat, arm, cartridge, alignment, etc. on tables B and D to observe the differences, the traditional level playing field.

But what if the arm was not interchangeable and could not be fitted to both tables or, more importantly, what if a given arm was not compatible with both tables? And then the same cartridge was not compatible with the different arms?

Then Solution 2 would suggest the best comparison would be between "systems" that were optimized for each table. True, you would be hearing influences of arm, cartridge, etc. as well but you would be comparing potential VS potential.

This applies through out the audio chain. Comparing one speaker against another without driving each by an appropriate amp would not identify the potential performance and thus differences between the two speaker systems.

Perhaps we need a tilted (compensated) playing field rather than a level one to make worthwhile comparisons?