I haven't had the same issues with AI consistency that I had back at launch, but I do still occasionally see head scratching results. Mind you I'm playing at 91 right now so maybe things get more consistent at higher difficulties.
As for driving advice on those more difficult stages, the best advice I can give is "slow is smooth and smooth is fast". Portugal in particular is a tough one. It combines constant close hazards with some of the worst grip in the game. The focus should be on those smooth corner entries. Even if you bleed time, you often (without realizing) make up time on corner exits, not to mention the fact that nothing slows down the car like crashing.
Of course that's an easy thing to say but a hard thing to do. I think my second best piece of advice is to forgive yourself for mistakes. Rally is a tough challenge, both in terms of skill and in terms of mental endurance. It's lessons are often harsh, but if you're patient, rewarding. Sometimes you need to walk away for a bit to absorb what you've learned and reset for the next stage or rally. And sometimes you just have to shrug and say "it just wasn't my rally".