I agree that this is a huge problem, but RNNs and CNNs aren't the whole of ML (random forests are a different category of algorithm). You should study the ML that has the prettiest math. Try VC theory, Pearl's work on graphical models, AIT, and MaxEnt as developed by Jaynes and applied by della Pietra to statistical machine translation. Hinton's early work on topics like Boltzmann machines and Wake-Sleep algorithm is also quite "deep".
Yeah, I suppose our instincts agree, because I've already studied all these things except the last two :-)
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