It shouldn’t have ruined anything except scaling for <big> and <small> tags, which should be avoided because they’re obsolete specifications that can be removed at any moment. <big> specifically is very bad because it will nest and scale infinitely if defined with ems.
I can probably change the <big> definition to a rem unit to prevent the exploit and allow at least some scaling based on the root font-size, but it still should be considered as relevant as the <blink> tag.