割(わり)にAlthough, Despite, Rather...for, Unexpectedly, Comparatively, Considering

Both ものの and 割に express contrast, but in different ways. ものの links two opposing facts to mean 'despite', e.g. '話せるものの、字は読めない' ('Despite the fact that he can speak, he can't read characters'). 割に describes a quality being out of proportion with something else, e.g. '高い割にはあまり美味しくない' ('For being expensive, it's not very tasty').

Both さえ and 割に convey, in some sense, a characteristic or event contrary to expectations. さえ is a strong 'even' that shows emphatic extremity or surprise, e.g. 子どもさえ分かる ('Even a child understands'). 割に expresses contrast with expectations, e.g. 年の割に元気だ ('He's energetic for his age').

Both are used in making comparisons, but に比べて is used to directly compare and contrast two things, e.g. このスマホはあのスマホに比べて安い ('This smartphone is cheaper than that one'), while 割に expresses a gap between expectation and reality, e.g. 値段の割に美味しい ('It's tasty considering the price'). The former makes a neutral comparison; the latter evaluates something against an assumed standard.

割に and にしては both express something contrary to expectations, but 割に suggests mild contrast with what was assumed, e.g. 高いわりに美味しくなかった ('For how expensive it is, it wasn't tasty'), while にしては more clearly emphasizes how something defies expectations for its role or class, e.g. 初心者にしてはうますぎる ('He's too good for a beginner').

むしろ and 割に both involve contrast, but from different perspectives. むしろ introduces a preferred or more accurate option, e.g. 寝るよりむしろ本を読みたい ('Rather than sleep, I'd rather read'). 割に shows discrepancy between expectation and reality, e.g. 安い割に美味しい ('It's good for how cheap it is').