Complaints which are general in nature don't get acted on. Rather, one needs to send a specific complaint about a specific incident on a specific date to the carrier, not to the ground handler.
I agree that sending complaints to senior officers is a fool's errand. Those are simply delayed while they are forwarded to the people paid to deal with them.
Of the issues you are experiencing, the only one I would raise is the boarding priority. The others all eppear to be dealt with when you raise them to a supervisor, so not sure why complaining is necessary. It also detracts from the significant issue, e.g., boarding later than you are entitled to.
Why not take your last experience and note that date and flight and to the extent possible, the name or description of the staff who sent you to the back of the line.