So you base one decent start with Parker on him being a starter, one questionable outing with River and he isn’t a closer, (even though he was a leader in saves a week ago). Brown is awful… You are making some leaps.
At this point, I would say the Parker or Perez over Brown has less to do with whether Parker or Perez have shown success in past and more to do with Brown showing pretty consistently he is not a starter. It happens - Chuck King during his career proved he could not start but amazingly solid in any inning with came after the number 1. Cam has some really great stuff - command of 3 pitches, mid+ 90's fastball, close to 15 mph drop in off speed - he just has to figure out where he fits in the game to make the level of impact he deserves - but it doesn't seem to be a starter.
We had a guy on our staff that totally changed his approach to the hitters if we put him on the bump first - because he felt like "had to get to the 6th" vs when he came in for relief, regardless of the inning, he knew he was there to be as good as he could be for as long as he could - but there was less pressure to hit a specific target.
River was never meant to be our closer - we have 2 guys on our staff that are here because of their ability to be what everyone looks for in a closer. The issue is neither can consistently throw a strike. If you remember what it looked like when Riley Ferrell lost it during the post season - there is little room for variability in release point with you throw 98-100 and when it is off, it is totally off the rails - hit the mascot bad. So River brings a bigger diversity than most closers but also doesn't have overpowering stuff - and I always expected him to be the main setup guy if not a potential starter one day.
When you push guys to do things that they are not built for - sometimes they start a new role on the team and sometimes they struggle. We have a lot of struggling with some key portions of our staff right now.
But in the end, we have to be able to score 5+ runs more often and against better teams than we have been playing or we are in trouble.