200 years ago in Japan, how much did accent and language very depending on class? Would it be easy to tell if someone was a peasant, a samurai or a daimyo based on how they spoke?

Absolutely. Keigo (polite language) is still very much a thing in modern Japan and from keigo alone you can tell who is 'above' and who is 'below' in a relationship.

Even if you know nothing about two people besides how they talk to one another, from the conjugations of verbs and how they refer to one another, you can tell who is the CEO and who is the secretary.

This is amplified in 18th~19th century Japan where the common folk had to use even more stratified words when referring to their superiors and more humbling words when speaking about themselves.

The formality of speech was also very much a thing for the upper classes and would be very distinct (for a Japanese speaker) from the casual speech of the lower classes. And of course, vocabulary, grammar, phrases, idioms, etc differed as well. Finally, the upper educated classes knew Chinese.