i'm connecting to a sharded cluster, without setting any of the w, wtimeout or j parameters. I've tried running an update command which alters a single document in the following ways:

from pymongo.write_concern import WriteConcern
dc1 = db.col.with_options(write_concern=WriteConcern(w=0))

db.col.update({"_id":"x"},{..}, w=0)
dc1.update({"_id":"x"},{..}, w=0)
dc1.update_one({"_id":"x"},{..})

but in the logs, i can see the exact command running with

writeConcern: { w: 1 }

The update is an increase on a field, and whenever there is a lot of activity and many workers try to increase that field they tangle eachother, and the command takes a lot to execute. I've assumed it was because of the writeconcern, and i've been assuming that disabling the write concern would make it faster, but it doesn't work.