“إِنَّ أَخَاكَ قَادِمٌ” may be suitable for a hesitant hearer or for someone expressing mild denial. It is therefore incorrect to label every sentence containing inna as exclusively ṭalabī.
The decisive difference between ṭalabī and inkārī is the listener's state. The same wording can occupy different rhetorical positions in different contexts.
For example, “إِنَّهُ آتٍ” may reassure someone asking “Perhaps he will come?” It may also counter someone making a mild denial such as “He cannot come!”