The type in question has since been renamed to CommandDataOption, as well as other such long types (https://github.com/serenity-rs/serenity/pull/1899).

With forced functional programming, you may be referring to serenity's builders? For example

    .send_message(|m| m
        .content("text")
        .embed(|e| e
            .description("...")
            .timestamp("...")
        )
        .components(|c| c
            .create_action_row(|r| r
                .create_button(|b| b
                    .style(ButtonStyle::Primary)
                    .label("press me")
                    .custom_id("button1")
                )
            )
        )
    ).await?;

In the next breaking release (`next` branch in git), we have a new by-value builder style which has turned out to be a better design in many ways:

    .send_message(CreateMessage::new()
        .content("text")
        .embed(CreateEmbed::new()
            .description("...")
            .timestamp("...")
        )
        .components(CreateComponents::new()
            .add_action_row(CreateActionRow::new()
                .add_button(
                    CreateButton::new(ButtonStyle::Primary, "button1").label("press me")
                )
            )
        )
    )

And a PR is open to make the API even better (replace redundant CreateComponents with Vec<CreateActionRow>) and more will be coming presumably.

Does this seem more rusty to you? We're open to more criticism - developmenet on serenity is quite active currently (e.g. 52 PRs merged in the last month)