I beg to differ.
As an experiment, I ran a character to 50 with no double xp, never did WST, only did each tf once, soloed missions.
At 50 I was fully slotted, albeit no purples, and had 242 million by converting merits to converters and selling them. No crafting, because I'm lazy, just sold all drops for 1 inf.
I regularly run Praetorian content, and converting and selling merits I usually have around 20 million by lvl 20.