The phrase "achievable only" is correct and usable in written English.
It can be used to emphasize that something can be accomplished exclusively in a certain way or under specific conditions.
Example: "This level of performance is achievable only through consistent practice and dedication."
Alternatives: "only attainable" or "possible solely".
Chess is not the only field where computers have achieved success formerly thought to be achievable only through human creativity.
On the basis of the analysis of human data on the activation of NST during cold acclimation, humans have the potential to increase their whole-body thermogenic capacity to achieve long-term weight loss currently achievable only through bariatric surgery.
The other emphasises a confidence achievable only with unconditional support.
It is probably achievable only with some significant restructuring of the management of central government procurement.
If you thought italic writing was something achievable only by ctrl + I, this is the style for you.
Moody's, a rating agency, says many have found funding "either impossible or achievable only at exorbitant levels".
It is a surprisingly difficult gesture to make, achievable only by using an odd combination of small muscles in the hand known as the lumbricals.
But the IMF also believes these lower levels of potential growth will be achievable only if interest rates are kept very low.
It is a plain, white monolithic chamber, but unlike most rectangular buildings it is seamless, a goal achievable only in concrete.
The first wave of garden cities and new towns demonstrate that the large-scale building of social homes is achievable only through good planning and governments that see housing as crucial to national welfare and social progress.
Consummation is achievable only in surrender to the metaphysical flux that pervades the universe, identified with death, though Wagner also sees it as regression to the state of unconsciousness before birth.
