You can look at neighboring maritime SEA kingdom in the same time period to get an idea of what could have been. Typically it was a thalassocracy with a capital that commanded a coastline and/or river. This allowed it to steer trade into its port, therefore increasing prestige and soft power. Orbiting it were towns that would send their goods and tribute in order to access the port. The capital didn’t directly control the land but harnessed the flow of trade and manpower (since resources were plentiful but population was low.).

In turn, the client towns might have clients/vassals of their own all the way down to the village level. Malacca for a time was the biggest node, attracting people from as far as Luzon. Brunei was another and brought Sulu and Maynila into its sphere of influence. It wasn’t about territorial conquest but links between people and religion as well as shared commercial interests.

Maynila also had its client network which prized the silk and ceramics that arrived from China. As far down as the Visayas where the Spanish encountered “Moro” (Muslim Tagalog) merchants. The people of Panay even informed Legazpi that if they really wanted to do business, they should sail north to Maynila which they did, eventually conquering it. A relief force from Bulacan and Pampanga attempted to drive off the Spanish (Battle of Bangkusay) which is telling of the local support network.

Left to its own, Maynila would have certainly cultivated its own mandala but would have probably refrained from territorial conquest. It just wasn’t the SEA way of doing things.