I'd say Starlight, but I think I'm being partial to my favorite pony, she learned identifiable lessons that you can apply in the real world, like when she learned that she shouldn't sell her friend's valuable and important things, when she learned to communicate better with her father, when she learned to establish rules and separate her work hours and free hours, when she learned that friends are not always the best option for a job, even if you want to be close to her, and most importantly, when she learned to respect other ponies.
For me a good role model is not the perfect pony that respects others, who knows when to say or do something, who is kind to everyone and has perfect morals, a good role model is the pony who learns to do it .
This, and the rest of what you've said is how I feel about the past few seasons, the series' concept about magic and friendship, and Twilight. They made Twilight an outgoing character, when you can't change nature, and her nature is introverted, but she was acting as an extrovert in season 9, and all of this 'friendship is magic' went from a metaphor to how your friendship with your friends can be magical, to be literal, and friendship now seemed like a weapon of defense, and Cozy Glow was right in saying 'friendship is power', because Twilight gained more magic power as the series progressed, and this power was closely related to 'friendship', and this 'friendship' is the reason why Twilight was crowned ruler of Equestria. Also, this whole friendship thing seems to be a mold, a doctrine, or whatever. Let's compare Sunset to Twilight, Sunset was a 'lost case' because she didn't accomplish the requirements of Celestia's 'ideal pony', who was expecting a pony exactly like Twilight, unable to think for herself.