Ἀγγελίαν, ὦ Σώκρατες, φέρων χαλεπήν, οὐ σοί, ὡς ἐμοὶ φαίνεται, ἀλλ’ ἐμοὶ καὶ τοῖς σοῖς ἐπιτηδείοις πᾶσιν καὶ χαλεπὴν καὶ βαρεῖαν, ἣν ἐγώ, ὡς ἐμοὶ δοκῶ, ἐν τοῖς βαρύτατ’ ἂν ἐνέγκαιμι.
What exactly is βαρύτατ’ eliding? It must be βαρυτάτην, but then the elision would be surprising to me, and the accentuation.
βαρύτατα, superlative adverb. The εν τοῖς has the effect of intensifying the superlative. It’s an idiom. It looks elliptical, and is sometimes explained as a cut-down version of (to take this particular example) εγω εν τοις (βαρεως φερουσι) βαρύτατα ἂν ἐνέγκαιμι, “I among those (taking it hard) would take it very/most hard.” (Note the presence of εγω.) But in practice it functions simply as an intensifier.