If anything, it's holding PHP back. I don't often work with WordPress projects, but when I have to, it makes me want to cry with how backwards they are. WordPress doesn't even have a real routing system!
Furthermore, its ecosystem just seems to encourage really, really bad things, like user-editable templates, PHP code "snippets" stored in the database, images which should be in themes stored as post attachments instead, and just general lack of respect for the idea of separating code and content. Almost every "plug-in" or template is crippled and begging for license fees and/or throwing spammy "notifications" all over the admin interface. I know this sort of stuff are more culture issues than code ones, but they're still problems, and ones you only really see happening in WordPress sites.
I get angry when a client comes to me with a bundle of WordPress mess and asks me to fix or improve something. It's shameful and disrespectful to take a client's money and give them a WordPress site in return. Do these people actually not realize there's far better things out there?