Learn English – is “you were sweet to help me / for helping me” the same as “it was sweet of you to help me”

C. John suggested helping Jane with the washing-up.

Consider some contexts in which this sentence might occur.

Julie asked John what she could do to speed things up. John suggested helping Jane with the washing-up.

Jane pointed out that Julie was old enough now to have some regular chores, and asked John if he had any ideas. John suggested helping Jane with the washing-up.

suggest VERBing does not imply that VERB has any particular subject; specifically, it does not imply that the subject suggests that he should VERB. Consequently, this sentence does not, as the quotation does, imply that John made an offer to help; it at most puts helping Jane forward as a good idea.

arduous has quite strong negative connotations: it is a word that you would use about a task, but not about a person's contribution to completing the task. It means difficult, needing a lot of effort and energy.

When the land rover broke down, we had an arduous trek to get back to base.

His duties are arduous and require a great deal of bending, squatting, reaching and lifting.

He had almost completed an arduous 16-hour shift when the accident happened.

A more appropriate word would be enthusiastic. Which in this context committing a lot of enthusiasm (energetic interest) to helping you.