No, not everyone is over 300 watts. Based on this:
Only the top 15% (or so, I’m eyeballing it) of men are.
I think the standard things to consider are nutrition and recovery. If you’ve covered those bases, then maybe you just have hit the point where 3-5 hours of SST can take you and need to mix it up. And, keep in mind that FTP isn’t the end-all be-all of cycling. Not by a long shot.