I recall hearing a few years back that User Benchmark was wildly unreliable where AMD was involved, presenting figures that made them look much worse than they actually were. No idea of the present situation. I also vaguely recall the “effective speed” rating being ridiculed (unsure if this is connected with the AMD stuff or not), and +25% does seem rather ridiculous given that its average scores are all over +50%, quite apart from things like the memory speed (the i5-2500K supported DDR3 at up to 1333MHz, the 5600X DDR4 at up to 3200MHz).
An alternative comparison comes from PassMark, who I think are generally regarded as more reliable. https://www.cpubenchmark.net/compare/Intel-i5-2500K-vs-AMD-R... presents a much more favourable view of the 5600X: twice as fast single-threaded, and over 5.3× as fast for the multi-threaded CPU Mark.