One workaround would be to export all Contacts to VCF, then prune the list to only those for WhatsApp, run it, let it import, then deny permission and then merge all the exports back into Contacts. But then that's only a keypress away from an accidental full-slurp and you still can't add newer contacts manually.
At one point in time, All AOL, MSN and ICQ really did was try to prevent orders from working on their network. ( AIM / MSN )
And other point ICQ were trying to turn itself into Yahoo, an internet portal.
Google Chat? It couldn't even get the basic right.
MSN started to displace ICQ when it was faster, better and Icons pack ( before Emoji ). And ICQ somehow manage to react to this threat by keep boating itself.
At some point before 2007, MSN won. AIM were still being used in US but the trend was clear, people were slowing moving to MSN in US while the rest of the world has switched away from ICQ to MSN.
Being Microsoft who in my mind has never created any decent product, thought they won and decide not to do much about it. It was the era before iPhone. The era when everyone would question, what is going to bring down Microsoft?
Then came the iPhone that shocked the world. Well least in broad sense of it. The UI were revolutionary. But the tech or dreams wasn't. Pocket PC, Palm, all had similar idea before and HTC were ODM at the time. We had a lite, useless, slow Windows Mobile that couldn't do much at all.
Everyone thought, surely linking MSN Messenger between the Desktop and iPhone / Android would make perfect sense?
Not at Microsoft. And when they finally did? It was too late.
Whatsapp manage to became the dominant platform because it was good and simple. Somehow the tech industry took nearly two decade to figure out.
You have classic desktop clients for all operating systems (e.g. Gajim for Linux and Windows) and there are clients for android (conversations) and iOs (Chatsecure). Most of the clients (pc+mobile) are open source. What's more, you don't need to disclose your phone number and the privacy enabled by OMEMO is great without any usability nightmares.
On top of that, the network is highly decentralized. There are many providers for free and paid accounts and you could also host your own server.
My understanding is Whatsapp took off outside the US entirely because it seamlessly used SMS when data was unavailable and that was certainly a killer feature in many parts of the world.
At least in large sections of the world. Businesses have WhatsApp numbers. You see it on signs everywhere. I now find it a pain that people back home in the US don't use it. I use it daily. I literally just typed a message on there 10 seconds ago.