In northern germany, we use the word "tüddelig" which means being slightly confused or having a tendency to forget things and it sounds extremely similar.
The meaning "clear" for tydelig came as quite the surprise for me :)
Wow, in both languages the words for "early" and "clearly" are only two letters off. Neat.
I am a native speaker, and in my opinion if it were "We clearly see him" then it could mean the same as "We plainly see him", which is like, "It is obvious that we see him." But "We see him clearly" means that our vision of him is not obscured or blurry, and plainly doesn't work at all for that.
I would take "plainly" as "simply," while "clearly" would indicate that the speaker understands what he sees, simple or complex.
Pretty useless adverb. Why not replace it with something actually useful like selvfølgelig, which is completely missing from this section.