If anything, your optimal design is just another mutation that may or may not survive time.
The fact that conditions change doesn’t make your current form ideal.
Speaking of conditions.
In 5 billion years there will be no need for natural selection cause Earth will dip into the exploding Sun and evolution game will be over. Nothing will keep working. Even in 1B years it will be pretty hot outside. We’ll have no time for that “optimal” crap anymore, starting now tbh, considering our stupid tribal nature and the complexity of overcoming it.
Btw, if we fail to continue our current civilization, there will be no another civilization, cause we’ve drained all under-your-feet resources long ago. The next civilization will be forever farmers slowly burned by a star.
We absolutely can escape this fate by finding something much better than a bare minimum.
Edit: messed up numbers, fixed
I disagree, evolution is not perfect nor intelligent (as far as we know). It's never the "best design" that survives, it's always "good enough for now", merely better than other solutions at the time. A billion years of good enough is not necessarily the best it can be theoretically.
I'm sure we can find examples of living processes that are dumb and inefficient, with obvious room for improvement, but have survived for millenia simply because it was good enough.
Of course you can. We could regenerate limbs like a lizard’s tail, keep growing teeth like a shark, not require so many different types of foods to survive healthily… The list goes on and on.
Which is the absurdity I’m pointing out.