The exact settings inside each presets of svt-av1 have been changing a lot between each releases.
The current latest version is 3.0.2 and to me the preset 6 is already looking not good.
(handbrake has 2.3.0 in current latest version)
But I agree preset 1 is an overkill, I'm more happy with preset 3's balance between quality and speed (as in version 3.0.2)
Although I say preset 6 looking not good, the artifacts are not very noticeable unless you pause the video.
And FWIW, handbrake uses "tune=0" by default. It says "None" but actually, in svt-av1, tune 0 means VQ (visual quality), tune 1 means PSNR (tuned for higher objective score but not visually good), SSIM is another objective metric.
Really you should only use tune VQ in real world use case.
So, if you are planning to use FFmpeg, you should add "-svtav1-params tune=0" in the options.