It changed, but not quite how it feels, before 2018ish, algorithms did more of the distribution work for you. Chronological feeds, real hashtag reach, less competition. You made the thing, the feed mostly took care of who saw it.
Now the algorithm is selective and skeptical. Your content competes against everything posted each day. The distribution work moved upstream into the creation itself. the 70/30 feeling comes from where creators look for the work. Cross-posting and scheduling get the focus. The biggest gains sit in the first few seconds of the content, before anyone thinks about posting at all.
The hook in the first 1-2 seconds, the retention cues, the pre-qualifying captions, the platform-native format choices. All of it is distribution work happening during creation