Sure, but here we are talking about 2 things here

1. the nsec.app flow (or any other provider) which IMO should provide a leaner option - specifically with no modals and no popups. 
2. the styled button to "bind them all" has a different purpose and yes, provide great utility as a drop-in solution. 

So yes, my "objections" is mostly to the modals/popups in nsec.app flow. 
I still owe nostr:npub1xdtducdnjerex88gkg2qk2atsdlqsyxqaag4h05jmcpyspqt30wscmntxy a proper github issue about that. 

In respect of the window.nostr.js button UX I would argue that in the  Standard Oauth user click on the familiar Google icon, does not have to type in your email address.  

But yes, how would the Login button know which provider to call without the address? 

Then maybe an option to just "pick a provider" and show a list would be nice, I guess.