I'm a former electronic warfare drone (Australian Navy) - I worked with radar and satellite primarily, though I also covered a myriad of other RF systems.
With your logic you also need to discount the southerly route not just because Malaysia and Thailand did nothing, but also because Indonesia never saw the aircraft. Further, Australian agencies have said they never saw anything even though the entire region is bathed in OTH radar. Not a peep from Keeling or Christmas island.
It seems more logical (from my background) that the aircraft went north, though until it is found it would be far more appropriate to assume nothing. The Inmarsat analysis is interesting, but it isn't boiler plate and the lack of intermediate ping data fuels suspicion.