This practical application of your advice depends on where a particular person sits in their social hierarchy.
E.g. an influential person that's a "hub" or "connector" in their social circle can switch from WhatsApp to Signal ... or insist on email only ... or insist on no email and only hardcopy snail mail (Donald Knuth) -- and others will follow their lead or accommodate them.
On the other hand, if you're one of the folks at the "spokes" or "edges" of social graphs... being defiant by deleting WhatsApp doesn't accomplish anything because others don't care to switch to reach you.
The above difference in social influence happens in Asia countries where many use WhatsApp beyond personal relationships for business to sell items or find work. If the business contacts you depend on for getting income use WhatsApp, you deleting WhatsApp just means you get $0 because they'd rather deal with other vendors who don't force them the hassle of switching to Signal. Power and leverage in social graphs matter.