if you compare single cylinder vs single cylinder, the larger engine usually has more power ( assuming both engines have near eqaul engine work ) but the larger ones efficiency and power per cc is drastically reduced as the cubic capacity gets bigger. which meens alot of times the larger engines dont run much better than a smaller one. now if you compare a 500 x1 vs 250 x2 there is no comparison as the twin is far ahead in power. 125 x4 would have about 2x more power than 500 x1. so you can never say 'theres no replacment for displacment' in a general term because it clearly isnt true. only when comparing apples to apples can the phrase 'no replacement for displacement' have some truth to it