There are several incorrect statements regarding WhatsApp in this post, and in this thread in general. It does have a desktop app which is fully synchronised with the iPhone. On the iPad you’re right that you’ll have to use it through the browser, but not on any Mac. No reduced photo quality as far as I’ve been able to tell, maybe in the past. When was the last time you actually used WhatsApp? You’re right about the lack of cross platform support, when it comes to transferring chat history between iOS and Android, but hey, at least you can easily send messages between the OSs. iMessage on the other hand is completely incompatible with Android other than sending messages as simple SMSs, lol.
Personally, I don’t like iMessage at all. The user experience is way better on WhatsApp, IMO. And frankly I don’t really care about Facebook collecting some data. There’s practically no way in this day and age to own, and fully take advantage of all, or most of, the features of a new smartphone while completely avoiding things like data collection and tracking. I reluctantly installed Telegram because some peeps are getting irrational and paranoid about Facebook collecting some rudimentary data, because sensational news stories have blown it way out of proportion. And if you’re already a Facebook user, or the user of practically any other social media app, it makes even less sense. I’d be far more worried about Google and 'big-tech' companies stifling free speech and doing political censorship ad nauseam.