Soo evolution doesn't always optimize for biochemical efficiency in isolation. Sometimes it optimizes the whole system, and "wasteful" metabolism can be the right answer if it removes a bigger constraint.
Birds have all sorts of optimizations that improve efficiency, some of which make them very different from mammals. Their lungs are different from ours in two respects. Firstly, they are relatively rigid and the pumping is done primarily by separate air sacs. Secondly, they have an outlet pipe so can take in new air while also expelling the old. The result is continuous oxygen exchange rather than a breathing-in/breathing-out cycle like mammals.
You can see the effect in how prey is eaten after a hunt. A mammalian sprint-predator like a cheetah has to catch its breath before eating what it has just caught. Its avian equivalent, like a Peregrine falcon, can immediately start eating.
They improve efficiency in their airborne and tree crown niches, whereas mammalian traits are optimized for their respective terrestrial or aquatic niches. And so on and so forth for every species.
Natural selection can only work at the granularity of whole organisms, since they're the things that compete and reproduce. There is no finer pressure on specific concepts like efficiency, except that they may help the organism survive - but whatever solution works for the whole organism, works.
More accurately: of populations of organisms, so long as there's direct genetic transmission throughout that population (e.g., sexual reproduction or possibly if sufficiently prevalent forms of horizontal gene transfer). Heritable differentiation which benefits the population as a whole will tend to be selected for, so long as those aren't overtly nonbeneficial to individuals, and may well explain various non-overtly beneficial adaptations.
> Soo evolution doesn't always optimize for biochemical efficiency in isolation.
How could it?
Evolution "optimizes" (as far as local hill climbing can go) fitness, which is the ability to produce viable offspring. Genes get mutated and then combined (in sexual species) and passed to offspring via reproduction ... that's the process that results in biological evolution, which is the change over time of the presence of alleles in a population. That's it -- there's no secret "evolution" sauce or engine. The optimization for fitness occurs through the environment affecting the relative survivability of traits--traits that increase survivability become more common in the population--this part is tautological.
You can see the effect in how prey is eaten after a hunt. A mammalian sprint-predator like a cheetah has to catch its breath before eating what it has just caught. Its avian equivalent, like a Peregrine falcon, can immediately start eating.