It is good enough. F-35's new cooling capacity is for all the electronics onboard, not just for the radar.
Let's say, AMCA's GaN TRM has 20 watts peak power. So at 300khz PRF (highest for the radar) with a pulse width of 1 µs it will have average power of 6 watts. So with 1530 active TRM, the aperture will have 9.1 KW of average power. And if assumed DRDO managed to achieve overall TRM efficiency (not PAE of GaN amplifier) at 20%, you will end up with 7.2kw of wastage. Which is well within the capacity of 10.5kw cooling system.
Rest can be used to cool back-end processor and other LRUs.
PS: afaik, radars barely operate at such high PRF. Though you can have lower PRF and higher pulse width.
Also not all TRM transmit at the same power. TRM at the edges of aperture area operate at lower power than those in the middle to optimise beam forming and suppress sidelobes. This is called amplitude windowing. So there is that.
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