I do not think you should generalise like that. My consultancy at (https://www.amberbit.com) has clients that are e-commerce sites, some really big and high-traffic. There is plenty of concurrency and OTP comes in exceptionally handy.
I am not involved coding-wise in either of these projects but from what I hear from my employees, they are doing a lot of data sync (in and out) with external services. Think, delivery services, currency conversion, payment systems, shipment tracking, stock management software. There are streams of data to process, and things like GenStage come in handy. In other places they benefit a lot from implementing circuit breakers as failsafe mechanism when something external fails, also exceptionally easy to do with OTP primitives.
I am also a big fan of GraphQL, but again, this is not something we use with e-commerce clients. Again think of product page, you probably want it server-rendered, served as fast as possible and as simple as humanly possible to be properly indexed by various bots (Google, Facebook etc.). As far as I understand the need for GraphQL is limited in the e-commerce store scenarios I saw.