Calorie burn problem: GPS vs activity tracking

I'm getting so angry with Fitbit's calorie burn!!!! I'm hoping that someone can make me make sense of this.

Basically, when I GPS track (phone GPS) my walk to work, it will state a certain amount of calories burnt. But then I'll track the exact same walk (via selecting it on my Charge 6, or letting it auto-recognise), and it will state DOUBLE that first amount of calories.

For example, from today:

GPS walk - 1.7km, 2309 steps, 76kcal burn.

Tracked walk (via watch selection) - 1.5km, 2151 steps, 199kcal burn.

There is a 123kcal burn difference! In the same walk! And the lower calorie burn is close to online calorie burn calculators.

The reason this matters to me is because tracking my activity is easier than GPS (remembering to turn it on/off, saving phone battery), and it also provides my heart rate data. When I GPS track a walk, it gives me no heart rate data (besides overlaying HR zones on the map).

And I know that it's tracking the HR data, because I can delete the auto-tracked walk, replace it with a manual entry with start time, minutes spent, and distance of my walk, and.... Voila! All of the heart rate data I wanted!

I also use the treadmill, and I can't be expected to manually enter every single walk/run I do on the treadmill just for an accurate calorie burn - otherwise what is the point of having treadmill as an option to track?

Additionally, I'm trying to lose weight, and having fitbit estimate hundreds and hundreds of calories burnt per day is really throwing me off my CICO goals. It's also crazy annoying with cardio load, and it's CONSTANTLY telling me to have a rest day.... I don't need a rest day, I'm doing literally half the exercise it thinks I am.

Sorry for the long post, turned into more of a rant than I thought. But does anyone have a similar problem? Or better yet, an easy fix? All of the posts similar to this seem to be pre-Google ownership (RIP), and just aren't relevant anymore.