Gmail works on like thousands of different software or services so the idea of Gmail being outdated or wrong it kind of a silly sort of thing to say because everything plugin or extension from say Chrome will work mostly just through gmail .
Outlook has a lot less options for software to work through it but still some can go okay together it as a whole but it can come slowly since all of Microsoft are badly coded for why they have said they actually use work Linux instead of Windows normally for work.
Yahoo I would agree is very out of date now not really any good except like dumpty or account which is not important to yahoo since it’s money problems have done more less no upgrades like 5 to 10 years meaning it’s very badly designed for business work as a whole.
Email, in general, is not out date or anywhere close to me this sounds strong like the question is being asked by a boomer or person with no technical knowledge if you even have basic tech knowledge you would emails are still as popular or useful as ever for example I close SEO clients most month by sending emails I doubt that will ever stop in my lifetime since everybody owns more less now.
Zoho is popular because it’s cheap and also can allow complex or good email send rates since emails build in spam checks don’t have issues when you use Zoho plus you can use it much cheaper than Gmail’s business rate of email which is good as well.