Surely for serious at risk user companies, options or initiatives exist within their reach and means @Tufan_Kaynak2, for their own sake and to benefit the whole community too -
One reasonable recourse is to collaborate via this forum on a collective action plan to contribute their support. The idea is to connect with others who share the same problem!
Clearly define and articulate individual multi-currency problem test cases in terms of actual and expected results, and submit these for all to review and respond to here https://github.com/frappe/erpnext/issues
For users that lack skills or resources, to expedite their problem resolution, they can engage the help they require
Certainly the code is best served by a plethora of automated tests, necessary and sufficient to gain and maintain quality control and insight to detect and fix code problems. But that will only result from committed users who recognize and support this requirement.
Your concerns are valid and appreciated but maybe rethink how to resolve your problem?