It must be a very small subset of English speakers for whom the word "excellent" can only be read in a Bill & Ted accent, so I suggest this is bogus argument.

Yes, it must be and yet 'excellent' is a really poor translation for this.

Perhaps "superlative".

Yep, that's (roughly) in the same vein as 'first-rate'. What makes the translation tricky (if you speak Russian, apologies for explaining the obvious) is that while the word has uses other than literal 'beautiful' it is composed of a superlative prefix and the root for 'beauty'. The line itself is spoken by character in a play, a high-minded, provincial county doctor as Chekhov himself once was. 'must be excellent¹' is strained and clunky in English to begin with and none of the more natural-sounding replacements evoke the connotations of the original.

¹ Moreover, nobody ever translated the name of the Russian fairy tale Василиса Прекрасная as Vasilisa the Excellent.