I note this can vary significantly between different institutions and possibly even programs. Unfortunately the reporting is very hit or miss, although College Kickstart is purportedly trying to compile those numbers for a few institutions from various sources:
Using those numbers, Georgia Tech, for example, had about 5600 EA admits between their two rounds, which per their CDS is out of 8413 total, so that is right around 2/3rds.
NC State had 13250 out of 18201, so that is actually a bit higher (about 73%).
But then Oregon was 18820/35377, so closer to half (53%).
For the most part I think this doesn’t matter–as long as you can get in your best application by the EA deadline, why not?
But I think if you identify some additional colleges of interest after their EA deadline, or perhaps (in rare circumstances) your application materially improves after their EA deadline, it is not necessarily a huge deal to apply RD instead.