Combination tires: both radial and bias ply?

[Big time]

If both radial and bias ply tires have both their benefits and drawbacks
why not them together?
I mean a tire with both radial and diagonal (bias ply) reinforcements?

Altough I've heard that racing radial tires are actually slightly bias ply tires as their reinforcements are slightly angled.

[Matra et Alpine]

As you noted they already take advantage of both approaches.
Once you start adding cross ply the tyre is no longer a radial

BUT, you can't have "pure" radial and crossply and expect that 1+1 = 2
it's like saying water is good for your skin and talcum is good for your skin and then mixing the two and expecting it better -- it doesn't

[LeonOfTheDead]

As you noted they already take advantage of both approaches.
Once you start adding cross ply the tyre is no longer a radial

BUT, you can't have "pure" radial and crossply and expect that 1+1 = 2
it's like saying water is good for your skin and talcum is good for your skin and then mixing the two and expecting it better -- it doesn't

+1, just for the example.
I guess you tried it yourself