Yes, but the idea was that Bisharp can still take on Jirachi just fine even if Jirachi is trying to paraflinch it.
Why does there have to be a perfect answer to a pokemon for it to stay in OU? This metagame is not about either having an answer to something or not, it's about what decisions you make so that your team is more or less prepared for each threat. In other words, it's not a binary "are you prepared for X threat yes/no," it's more like a continuum of preparedness. As
Agent Gibbs put it, "the era of being able to run universal counters to the metagame's top offensive threats is long gone."
Moreover, the pokemon I suggested (Garchomp, Char X/Y, Bisharp...) are good for much more than just hitting Jirachi. You wouldn't be carrying "a cleric on top of a counter to handle one pokemon," you'd be carrying two good pokemon that just so happen to help out against Jirachi, as well as with other things. The goal is to make a team where all the pokemon work together, rather than individually each focused solely on their own threats, to minimize the amount of things that the overall team is weak against.
So no, you don't have to bring a cleric if making room for it would detriment the rest of your team. But if you find your team is weak to Jirachi and in your experience Jirachi is common enough to warrant preparation, then you might need to think about what changes you could make so that your team loses as little other coverage/synergy as possible while gaining some coverage vs. Jirachi.
By the way, only keeping things in OU that have perfect single-mon counters would actually exacerbate your complaints about the game becoming matchup dependent. That is how RPS works, after all. Rock is a perfect counter to scissors, scissors is a perfect counter to paper, paper is a perfect counter to rock.