There are several factors affecting sharpness. The image has backlit subject which is very difficult to have in sharp focus with so much in shadows. Try on a well lit subject.
I have used Tamron Diii 150-500 with Sony A7IV before moving to Sony 200-600.
What I have found is that Tamron lens had better stabilization compared to Sony. Maybe because the Tamron was released in 2022 and may have better tech than old Sony lens.
Also of note is that both lenses are sharpest at f8 throughout the zoom range.
I use mode 1 for most handheld photography. Still figuring out the best mode for different scenarios.