How far are the Oregairu mangas from the original source?

It varies. Some parts are very close, while others have some noticeable differences.

Overall, the 'Oregairu' monologue manga is a decent adaptation. It keeps the main plot points and character developments from the original, but there might be some minor differences in the way certain scenes are presented for visual effect.

I'm not sure exactly, but it seems to have a decent lead compared to some other series.

Not much. The Danmachi manga mostly sticks close to the source material.

Overall, the Invincible comic sticks closely to the original. There might be a few minor tweaks for better narrative flow or visual presentation, but nothing major.

It varies. Sometimes it follows closely, but there are some creative liberties taken to make it more appealing for the manga format.

Not much. The Berserk manga mostly sticks close to the original concepts and storylines.

It doesn't stray too far. The Re:Zero manga mostly adheres to the key plot points and character developments of the source material.

It doesn't deviate much. The manga mostly sticks to the key plot points and character developments of the source material.

It varies. Some Lezhin Comics stick closely to the source, while others might take more liberties.