Part of the reason for the disagreement here is the OP chose to characterize the late season additions as "ringers."
As the term is usually used and defined, a "ringer" is someone who belongs at a higher level of competition and is brought in, usually under an assumed name, to dominate a lower level of competition.
For example, in the 1970 movie M*A*S*H, Fred Williamson is a ringer, a former professional football player, who is brought in to the second half of a "friendly" football game among doctors to win a contest on which a lot of money had been wagered.
The term comes from "dead ringer," that is, someone who can be an imposter for a legitimate player. When you bring in a "ringer," you are cheating.
The meaning of the term is carelessly expanded to include adding any good player, even if the player is eligible and legal in all respects, to a team just before a match.
I maintain the position that any coach is entitled to improve his team in accordance with the rules of the contests, leagues, or tournaments he enters.
Improving your team by adding legal players is not, in and of itself, "bringing in ringers."
Yes, there are teams out there that employ over-the-top tactics to field teams that can win tournaments and garner worthless accolades.
There was no suggestion in the OP that this sort of excess was going on here. There was no mention at all of how well the team did with the addition of these new players.
The coach didn't bring in Bryce Harper. He replaced some starters to "close out the season." This isn't a big deal.
It's unfortunate the thread started with an imprecise use of a loaded term.