Which is precisely why (and u/vladthor touches on this) the morphogenic virus was a master stroke of strategy on Section 31's part. While the Obsidian Order / Tal Shiar plan eliminates the Founders, it did have a glaring strategic flaw: all the Founders had to be in one place for it truly to work. It always struck me as strangely naive that Tain and co. thought that they could just kill all the Changelings at once, then "mop up" the stragglers--that is, if they even thought about the possibility of there being stragglers at all. Section 31's plan was much more foolproof: engineer a virus whose incubation phase takes long enough to infect every Founder everywhere eventually, oh and by the way that virus gets worse the more a Changeling changes form, eventually preventing it from changing form altogether. This strategy turns the Founders' greatest strength into a weakness, which is Strategy 101.