Yes, the Prophet Muhammad ﷺ spent ~13 years in Makkah calling people to Tawheed. That doesn't mean that the default for every Muslim community in Dar al-Harb/Kufr is in the "Meccan stage" of "Da'wah." The Shari'ah and Islam were perfected by the time the Prophet ﷺ died. It is that perfect/complete form of the Shari'ah and Islam that every Muslim has inherited and every convert must accept. There's no "going backward" to a "Meccan stage" of Islam for anyone, ever again. The only way for a non-Muslim to permanently end his state of war against Allah ﷻ and His final Messenger ﷺ - without becoming Muslim - is to accept the application of the Islamic Shari'ah. So, why would anything less than full acceptance of Islamic Shari'ah be accepted from a convert to Islam?

Looting in Dar al-Harb is only prohibited for the Muslim that has a guarantee of security that is in effect according to Islamic law. Dar al-Harb must accept that Islamic law is in effect in order to benefit from the dictates of guarantees of security from Muslims. Also, authorities of Ahl al-Harb must refrain from detaining or arresting Muslims. Once detained or arrested, by agreement of Ahl as-Sunnah, a Muslim is no longer bound by a guarantee of security because Ahl al-Harb violated it. Authorities of Ahl al-Harb must refrain from restrictions on the wealth and property of Muslims. Once the wealth or property of a Muslim is seized or otherwise prevented from transfer, they have violated the guarantee of security and it is no longer in effect. Looting in Dar al-Harb is absolutely permissible in a land where Muslims are not allowed to practice Islamic law, Muslims are subject to detention and arrest, and Muslim wealth/property is allowed to be seized or restricted from transfer.