Its not the WD40 that gets gummy, its the stuff it loosens and holds in suspension until the carrier evaporates off. By not really cleaning the gunk/WD-40 out you end up with.....gunk. I have cleaned mechanisms with it, well flushed and/or wiped off and reassembled for (way too) many years and, if I have done my part as a careful workman, I have never had these oft repeated gummy residue or waxy film issues.
That said, I do agree that there are number of newer generation products that do as well or better. Also the lubrication barrier it produces is not for high pressure applications and will break down allowing metal to metal contact under high load. Some new-gen products can do this better, though Im still a proponent of using various weight oils and/or greases in different areas of an assembly specific to their requirement rather than just hosing something on and saying GTG. Yes, Im 'old school', but my stuff lasts about forever and when I have had opportunity to mic components and watch/measure over time and use they have shown -0- wear; works for me, YMMV.