That remark, while truthful a long time ago, didn’t really apply during the later periods of IE, or the early periods of Edge before it became a webkit clone. When it needed to win back users, there was a lot of focus on standardization, meaning that when I worked on sites, I tested them through MDN Docs, and in Firefox and IE first, made sure my solutions were not using any -webkit- nonsense, and then they would be fine on other browsers. Anytime I did find IE bugs late in its life, it was usually because some other browser coder was not correctly following standards.