With Google's new update, do you think guest posting is a waste of budget now?

If you create content for people, not for acquiring a backlink, then it's not a waste. With the right host (relevant website, relevant audience, a website that has readers - not just clicks) you can get a huge value form it. At the end of the day, it's value you put on the table that attracts leads.

As long as the content is truly informative, we can't say guest posting is a waste of time. But the way some are doing it now is considered "spamming". Google is giving more and more value to "users' needs" and we should keep that in mind when guest posting.