They haven’t ‘survived into this day’ at all. They’re essentially a 20th-century creation, from a time when people were paring down classical & baroque performance styles to a less indulgent, crisper, lighter manner, thoroughly unsuited to many big-fat-diva sopranos. You’re right that neither is authentic, it simply comes down to preference. A lot of people prefer them.
And, of course, there’s now plenty of new music written specifically for countertenor - take a listen to Britten’s Abraham and Isaac as a good example
I posted exactly why they still exist, and I did it in the very first response to the OP.
Take the time to read and accept it. It might not be a reason to which you assign much value. If you wish to “debate” the relative merits of counter-tenors, then take it to GD.
