Yes, PES has always been this way. Stats are irrelevant to CPU controlled players, and their stamina is endless.
When the CPU is losing, rather than changing tactics or formation to try to force a goal in a plausible and fair way, it simply gives itself what is essentially a stat boost and starts pinging around perfect, high-speed, laser-guided passes and every CPU player suddenly develops impeccable ball control and dribbling skills and get an obvious boost in their acceleration. Any tackles you make during this phase will result in the ball being continually deflected conveniently straight to another CPU player and your keeper will also become next to useless. Meanwhile, your players become noticeably sluggish, lose the ability to pass the ball 5 yards and start stumbling all the time.
And in recent editions, the CPU can blatantly foul you but the referees often ignore it, but the referee will regularly call fouls against you when you make minor contact with a CPU player but don't even tackle them.