Apple doesn’t own the alternative apps like WhatsApp, Messenger, Slack, etc. Those are the apps I was talking about, if those apps aren’t good enough for business use (they are, and are used widely in business), then that’s the apps problem, not Apples. See, that’s what I was saying, not that it was a problem with iMessage, not Apple.
And you absolutely can use Teams, Slack, etc. for standard comms within a business setting, plenty of people do it. And it doesn’t have to be default. If you’re talking about where codes for two-factor authentication or things like that fall, that really doesn’t make any difference. Besides, most two-factor authentication allows you to set an email account as the destination for the code to be sent to, which can be linked with several of those apps as well. Besides, even if you had to receive two-factor authentication codes in iMessages, so what, you grab your code from iMessage? Most if not all of normal back-and-forth messaging can be done via apps like WhatsApp, Slack, Teams, etc.
I’m not saying it would be bad to be able to set a different default, but I don’t think it would really make much difference. You can just choose not to use iMessage for any of your normal messaging needs.