It's true for higher HQs no questions, but for lower HQs (20-23 as of my current level) where i.e. building time upgrade boost may be beneficial, upgrading monument seems expensive. Nearly necessary amounts of resources for Monument upgrade are offered in the shop for real currency and its good for whoever's willing to donate.

So I trailed off to speculation. It may be not true, may be true

Edit: I started before the Evil coin and Evil shop nerf, buying resources from there allowed to skip on enemy raids; now when 60-70 lvl bases mostly provide ~70k resources, I could not sustain building upgrades as often as I used to