Can I stay for 5 years on a DTV visa while traveling in and out of Thailand every 6 months?

Yes 5 years visa. After 180 continuous days, you have 2 options.

1) Exit and come back to get another 180 days

2) Apply for extension at Immigration. When you apply for extension, you will need to submit the entire set of the documentation you used originally when applying for DTV. It’s like applying for DTV itself again. If there are any discrepancies, your extension might get rejected. Heck they might even craw back your original DTV if they found out it was misrepresented or invalid eg you no longer sign up at your favorite cooking class. Additionally, there might be tax implications staying past 180 days.

Tell me again why anyone would consider extension?

The general consensus is that extending in country is very difficult and not worth the hassle.

You can max stay 180 days pr entry. But you can come and go as you please and everytime you come back you get another 180.

Yes

You can leave whenever you want sub 180 days and it resets when you come back. Ive done multiple few weeks/short months, left, came back and it always resets.

Exit and return every 180 days for the full 5 years to save yourself any hassle,

You can

You can extend for 180 days for every entry to make it a total of 360 days.