Not even remotely true. REST was a re-invention of XML-RPC wheel -- for the web and using baroque HTTP conventions that were meant for documents and hyperlinks.
XML-RPC was never rejected because it never caught much on in the first place. On the enterprise they pushed for SOAP at the same time, and on the web it wasn't yet a period were anybody really did rpc (plain AJAX, REST or any other kind).
In terms of simplicity it goes like: XML-RPC -> REST -> abyss -> SOAP, with XML-RPC and REST both on the far "simpler" end of the scale compared to SOAP.