I think this is fundamental design difference between SQLAlchemy and ActiveRecord in general. SQLAlchemy uses Data Mapper pattern which does not necessary map 1:1 to the row in the database, so you have to deal with the whole (Object, Mapper, Data) tuple instead of just Object in case of Active Record pattern (of which Rails' ActiveRecord were based on).
This means SQLAlchemy does not try to hide away SQL, which is beneficial in dealing with complex queries. In Rails ActiveRecord you could use arel in such case but being a query builder it lose the benefit of ActiveRecord, whereas in SQLAlchemy it could be done relatively easily within the ORM layer (arel equivalent in SQLAlchemy would be its Expression Language). On the other hand, some things that are complicated in ActiveRecord can also be trivial to implement in SQLAlchemy (e.g., column_property[1])
This means SQLAlchemy does not try to hide away SQL, which is beneficial in dealing with complex queries. In Rails ActiveRecord you could use arel in such case but being a query builder it lose the benefit of ActiveRecord, whereas in SQLAlchemy it could be done relatively easily within the ORM layer (arel equivalent in SQLAlchemy would be its Expression Language). On the other hand, some things that are complicated in ActiveRecord can also be trivial to implement in SQLAlchemy (e.g., column_property[1])
[1]: https://docs.sqlalchemy.org/en/13/orm/mapped_sql_expr.html