No Greek Lexicon is infallible or inerrant. This is one example because they tend to suggest that ancient languages had no etymology. Ekklesia is just such a word.
The usage and symbolism of the word is deeply embedded within Greek culture and would have been known to the Apostles, Disciples and Early Church Fathers. In its original usage it was the term used to assemble or call out the army. It later was extended to the assembly of the voters or electorate. This was not a general call, but a specific call to a very limited number of persons (those males over 18 who had served at least 2 years in defense of the city) and for a very specific purpose. A proper translation is convocation.
In the usage within the New Testament it is not a general call to a a body of believers, but a reference to a convocation with a hierarchy and a specific purpose. Jesus first formed His ekklesia from among the disciples, these were his Apostles with Him at the head. He later build His Church upon St. Peter with Himself as the chief architect.
We’re saying the same thing but focusing on different things.
You see a car and see an engine. I see a car and see a drivetrain. We’re both right.
The church IS the body of believers. And it has a hierarchical form of a sort. Paul evern refers to it (what kind of person can be a deacon, etc. But the hierarchy is only an attribute of the church.
I’m working with some relational databases right now. To use it as an analogy, the database is the “body of believers”. The interconnectivity (keys, indexes, information used to create universes, etc.) could be the hierarchy. But the database itself is the body of believers, and keys and indexes are also individual data elements (believers).
The hiearchy is a way of “arranging” them, but the individual elements (believers) are what make up the church.
And the analogy is of course not perfect, since believers have a direct and personal relationship with Jesus. That said, you need some sort of hierarchy to schedule bingo games, picnics and handle the openly homosexual music director.