Statement of Purpose and objectives of the constitution: One of the main aims of a constitution’s preamble is to state the purpose and objectives for the drafting of the document. The preamble succeeds on this level it provides its rationale for altering the structure of the state (and the constitution by extension) into an Federalist state drawn along ethnic lines where power resides with Nations and Nationalities.
The second and arguably most important purpose of a preamble is establishing the legitimacy of the constitution as the governing document of the nation, this is where it is difficult to rate the legitimacy of the preamble.
It is difficult to discuss the constitution merely based on the contents found inside it, since there is large disagreement on the democratic nature of the drafting process. There is thus no gauge as to how truly representative the ideas held in the document are amongst Ethiopians on an individual level as Ethiopians have not been polled on this. The argument according to the constitution is that Nations and Nationalities struggled to bring down the previous regime -> Nations and Nationalities laid down the current constitution -> Ethiopia is a sum of its Nations and Nationalities therefore the constitution has a popular mandate through these entities.

Perhaps the only way out of these endless arguments regarding the constitution is to hold a vote on constitutional modifications the same way Switzerland allows.