with the right contact points almost any body position can be achieved. It will probably by fugly as hell, and may not handle very well, but it is possible.
Caveat that this may only possible on traditional bikes with rounds seatposts and steerer tubes that open up the full range of aftermarket options.
What you are describing was exactly how the tri bike was born. Many early converted frames did in fact look a little crazy until purpose built steep seat angle bikes began to be developed. Tube shape is a secondary thing to proper geometry for purpose. Something I am finding interesting is that now that the weight of aero bikes can get down to the UCI weight limit we saw pros using full aero machine on some of the steepest climbing stages of the Tour. This in a way reinforces what I feel that you are saying and I am attempting not further clarify, that it’s geometry. What I mean is that the major difference between a climbing race bike and an aero race bike is tube shape. The geometry is the same for all race bikes within a narrow range of head and seat angles. Aero bikes climb just fine they just tend to weigh a bit more but these days if you have the budget they can be built pretty light without Gucci parts.
That’s not surprising. You can get a disc brake road bike with expensive, but standard parts way below the 6.8 kg limit. Canyon sold a ~6.0 kg disc brake bike something like 5 years ago, Specialized sells the Aethos. That easily leaves you with >= 800 g to add aero features, which doesn’t seem too hard.
The 6.8 kg weight limit is yet another rule that promises “safety”, I guess, but hasn’t kept up with the times.
It isn’t that simple. You cannot move all contact points by the same amount, and this means you cannot achieve the same body position exactly. The cranks are fixed, and changes in the saddle position are relatively small. You have the biggest leeway with stem length and handlebar width.
In my case, the proper sporty fit on my endurance road bike was achievable, but it forced more rotation of my back, which put more pressure on my perineum. I tried to rotate my saddle forward, which led to me sliding off of it, and buying new saddles with cutouts (which helped somewhat, but still isn’t as good as my more aggressive road bike).
Moreover, even when you achieve the same fit, you will have different centers of gravity, which leads to different handling and a different ride feel.
A saddle can be moved back and forth 50-100mm with standard rails and changing between layback inline and straight and even a layback seatpost fitted in reverse.
If you weren’t able to get a “sporty” fit on your endurance bike that’s by design of the manufacturer fitting parts with limited range of adjustment to sell more bikes.