Perfect grayness, for typical text, is possible only at the expense of ugliness somewhere else. Clearly, allowing arbitrary hyphenation will make perfect grayness much easier, and forbidding hyphenation will make it much harder.
Conversely, relaxing grayness would make perfect hyphenation (i.e. none) much easier.
Typography can often be improved by rewriting to fit the context (measure = text width, and location on the page).
TeX's big achievement in line breaking are, in my view, the use of dynamic programming, and the care, experience and diligence applied to the many details involved in the problem.
A large part of the art of typesetting is the art of breaking things, but gracefully. Best results will always require an element of hand adjustment, but TeX does a good job automatically, most of the time.