Ummnn...it's not that simple, but I'm getting what you're trying to say. The answer is both yes and no.
In terms of basic fuselage the AMCA won't be any different than a LCA except for two or three coatings. A specialized primer for RAM, the RAM itself and a top coat to keep weather away from the RAM. But the actual designing of it would be extremely difficult. Take any stealth aircraft, KAAN for example
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See how all different surfaces try to stick to just two or three different angles; this is just on the macro level. On micro level all the small surfaces, every curvature, all protrusion try to follow this as much as possible. And the more stealthy a platform becomes the less aerodynamic it gets (see the example of F-117) and vice-versa. So now you're constantly at this tug of war between aerodynamics and RCS. And this thing is difficult.
Now coming to your question of why are we waiting for stealth tech to come up first instead of just moving forward with the technologically simpler parts then the answer is yes, we're trying our best.
View: https://x.com/HALHQBLR/status/1547164027062976513
But so much is there from releasing of funds to size of actual funds to uncertainties with engine...