The realities of game development mean that sometimes, even with delays, when you have a game as expansive and as ambitious as GTA 5 a few corners simply have to be cut to make ends meet.
The game's launch was pushed back a few times, Online was released separately and the ports also suffered delays, however the fruits of the wait are obvious. Grand Theft Auto 5 turned out to be one of the best optimized, most polished, least buggy game of the past three years, not to mention it has some of the most content among AAA releases.
But. And it's a pretty big but. No game, no matter how polished, has ever reached the elusive status of "perfect" (let's not get bogged down on an existential debate about whether or not perfection as a concept is even attainable or not, shall we?), regardless of how close it got. There is a reason why GTA V is still making headlines three years after launch. There is a reason why Online is among the most played multiplayer games today.
The cops aren't that reason. In fact, the cops in GTA 5 are one of the few aspects that drew steady criticism from fans and the press alike. Many fans of the franchise who played older titles, notably GTA IV, were a tad baffled to find the cops in GTA V have devolved instead of evolved in spite of pretty much every other feature being improved.

Really, Rockstar, mate, we absolutely love your game, and it deserves every one of the countless awards it has won over the years. But the cops? Like, couldn't you have at least lifted the system from GTA 4 and just patched it into 5's code? The police in that game may not have been the toughest opponents, but they had search areas, they were dispatched to the scene of the crime and they employed tactics.
Replacing the relatively smart and realistic Liberty City Police Department are the genetically engineered, mechanically augmented super-soldier-wizard-demon fiends employed by the over-funded paramilitary group masquerading as the official police department of Los Santos. Or something.