Health app steps count is less than Fitness app

The Health app on my iPhone continuously shows lower steps counts than my Apple Watch or the Fitness app on my iPhone. The devices priority is set as follows in my iPhone Health app:

NOTE: Everything from the "Health" one and below are old inactive devices or connections. I use my old Apple Watch 2 when my new Apple Watch 8 is on charge.

These issues have been happening for years but I blamed it on 5+ year old devices. Now that I have a new iPhone 14 Pro and a new Apple Watch Series 8 I expected them to work properly. They still don't. I've followed every thread in the Support Community on this specific issue for years and no solution has been found that I can see.

I ran my own little test last night. I've provided screenshots for reference. The step counts in question are circled in yellow.

8:10pm - I sit down and don't move for at least 5 full minutes. I then get my phone and begin to check the apps.

8:18pm - My step count in the Health app is 7987, in the Fitness app it's 8086. A 99 step difference. I then stand, with my Apple Watch 8 on my wrist and my iPhone 14 Pro in my other hand, I take exactly 100 steps and swing my arms the same speed and distance.

8:21pm - My step count in the Health app is 8087, in the Fitness app it's 8186. A 99 step difference. Both apps show an overall increase of exactly 100 steps, but if we look at the minute-by-minute breakdown, it shows the watch recorded 100 steps and the phone recorded 48 steps.

I leave both devices overnight to see if the figures would eventually sync up.

8:08am (almost 12 hours later) - I go back to check the final step count. My step count in the Health app is 8193, in the Fitness app it's 8275. An 82 step difference.

This was just one test, but it's been this way for years and the amount they differ between apps varies. I could understand the Health app showing a higher number of steps than all other devices and apps because it is meant to collate all figures, but it makes no sense that the step count is less.

Why are these numbers still not consistent after years of app and device development? How do I get this fixed?