I agree with you that it would be better if Temania were not such a large landmass but I think it is something we just have to work around, primarily by emphasising the population of the country would be concentrated near to the coast. I am personally not convinced by the other points you make though.
Regarding the prevalence of Ahmadism, the situation is parallel to real-life. Temania is actually closer to Medina in the game than Malaysia and Indonesia are to Bangladesh in real-life. As with the spread of Islam to Southeast Asia in real-life, I think it is reasonable to assume the spread of Ahmadism to Temania was through a combination of trade and missionary work. In addition to the Ahmadi polities in Majatra, this could have been due to influence from the
Asli Sultanate too.
In my opinion, the case for keeping a country inspired by Indonesia and Malaysia in Temania is strong. Yingdala was a colonial power in the region and is located reasonably nearby, which makes sense when you think about the real-life influence of China (on Malaysia in particular). Approximately a fifth of Malaysia's population is ethnically Han Chinese. Perhaps more importantly, Indian-influenced states played a central role in the history of both countries. Temania being located close to Vascania is realistic then.
In more general terms, Temania is located near to countries based on Vietnam (Kimlien) and Thailand (Hanzen). Both of these countries are geographically close to Malaysia and Indonesia in real life. Though it is sometimes difficult to quantify "shared cultural tradition", I think it should be clear that there has been a significant degree of interaction between the peoples and polities of these regions over a period of many centuries.
In terms of language, Temania is in a realistic position too. In recent role-play, I have sought to provide some
background to the distribution of the Austronesian languages. In the game, I have suggested these languages originated in Dalibor and were spread by a series of migrations. The concept is inspired by the real-life Austronesian expansion. Having most of the
Malayo-Polynesian languages in Temania and Tropica matches approximately with their geographic distribution in real-life.
In addition, I would like to specifically object to the proposal to move these peoples to Seleya. In my view, you have personally done good work in helping to improve the cultural protocols of the continent, specifically by introducing various indigenous peoples of South America. Seleya being primarily based on the Americas is realistic and coherent (though I acknowledge there are outliers, principally Aldegar). I do not object to the inclusion of Filipinos in Tukarali due to the existing role-play history that justifies it but I do not think it would beneficial to add more Southeast Asian peoples to the region.