That saying is an example of armchair quarterbacking. Like today, successful designs were copied and re-engineered to yield something that might earn as good a reputation as the original (people don't copy crappy designs intentionally).
The Springfield 1903 was a good example of a state of the art combat rifle of the early 1900s, even though it was a copy of a great combat rifle, the Gewehr 98. It became a target rifle after WWI due to the Army target team using it instead of the much heavier M1917 Enfield (which was actually a modification ofthe P14, England's design to replace the SMLE).
The K98k was a refinement of a successful design, the Gewehr 1898, and was one of the best (if not the best) bolt action battle rifle ever invented. Its durability, accuracy, reliability, and ease of maintenance are wishbook items even by today's standards.
The Lee-Enfield was a much-refined design dating back to the late 1800s, and had its share of problems, but it was a good serviceable rifle and the main battle rifle of the British Empire and Commonwealth nations (not because it was superior in any way, but because the British supplied arms to these other nations).
The Mosin-Nagant 1891 was a joint development of several nations, manufactured in several nations originally (notaby France and the USA), retired before WWII, then re-introduced because it was cheaper and more reliable than its replament. It is also a very serviceable rifle and infantryman-resistant.
Note also that of all these rifles, the only design that enjoyed a commercial revival was the Mauser 98 design.