So the current common wisdom for 5th ed 40K is that mech is king. There are a number of common explanations - cheaper transports in newer books, improved vehicle survivability in 5th ed and less punishing transport rules.
Consider an army like the Imperial Guard. A bunch of T3 5+ save guys. Should they go around on foot, or take a relatively cheap armored transport with two built in heavy weapons and the ability to fire up to five weapons out the hatch? It seems like a pretty obvious choice, but should it be?
Are there other considerations outside of the rules that lead to some builds being "king"? Can we as players do something about it outside of our own army lists? If so, would it really matter?
For example - terrain. Are the boards we play on too mech-friendly? Would denser terrain and more dragon's teeth on the field help fight the trend? Or would it just give rise to builds featuring skimmers and indirect fire as the new kings? Do standard missions/deployments contribute? What else?
What do you think could be done to mix up the "meta", to allow for a variety of armies and builds to be competitive at all levels, other than changes to the base rules or codex rules?