why is colonialism not considered to have impeded the growth of Southeast Asia the way it is considered to in India?

I'd have to say I seriously doubt this assertion. Especially when referring to the Philippines in particular. The distortionary effects of the colonial and postcolonial economic and political regimes in the Phillipines are very widely discussed here in the country and in the literature. In particular the Bell Trade Act, which was passed in the Philippines two days before independence but effectively tied the country's economy to the US, and very specifically the sugar and tobacco quotas for Philippine exports to the US have been regularly cited for decades as a distortionary post-colonial legacy in the Philippines that shaped both the economy, and contributed to maintaining the shape of the political system.

In addition the Asian tigers of Japan, Taiwan, and South Korea, aren't postcolonial in the same sense other 'postcolonial' societies are. None of them experienced long colonial regimes from European powers.