The phrase "as the only reasonable" is correct and usable in written English.
It can be used when you want to emphasize that something is the sole logical or sensible option in a given context.
Example: "After considering all the alternatives, I concluded that this approach is as the only reasonable solution to the problem."
Alternatives: "as the sole logical" or "as the one sensible".
"Nick really has emerged as the only reasonable voice on Europe," one ally said.
This is most apparent in his revisionist championing of Cleon and other Athenian hawks, whose policies he consistently presents as the only reasonable choice.
(Men choose Hamlet because every man sees himself as a disinherited monarch; women choose Alice because every woman sees herself as the only reasonable creature among crazy people who think that they are disinherited monarchs).
They see a retroactive approach as the only reasonable option, because resolution authority is supposed to be an extraordinary power used infrequently, if ever — and the amount of money will always be unknown until it is needed.
Many central bankers continue to see low and stable inflation as the only reasonable goal for policy, while others argue that inflation moderately above target is an acceptable price to pay for a stronger recovery.
While Republicans are likely to demand an up-or-down (and largely party-line) vote on Judge John G. Roberts as the only reasonable course, the purposeful disenfranchisement of those of us who are not part of the president's right-wing religious base should be reason enough for Senate Democrats to use the filibuster to block this nomination.
There clearly is such a boundary, but by talking as if there were none, religious ultra-liberals and agnostics (the "fluffy brigade" as I affectionately call them) manage to make it look as though the only reasonable position to take in this debate is one where the sole passionate commitment is to a lack of passionate commitment.
For Deutsch, who accepts it as true, the only reasonable explanation for the QPT is that the many worlds interpretation (MWI) of quantum mechanics is also true.
We also point out that, among the different possible ways to approximate the two matrices and as diagonal, the only reasonable approach is setting their offdiagonal elements to zero.
Parenting advice about divergent toilet-training methods (not to mention plenty of other child-rearing questions) is typically dished out as if it were the only reasonable, reliable option.
So with regard to health, whether or not we can have it all, the only reasonable way to have as much as possible -- is to try for exactly that.
