There are many things about the Scaled Agile Framework(Safe) I don't like, but rebranding sprints to iterations is something that I really like. It's not about being faster, it's just about time-boxing development activities and making planning, communication, demoing and retrospection a routine part of your team activities within that time-box.
Totally agree, the goal is to timebox features and tickets.
If the feature or task takes longer than the allotted time, you get to be agile and reevaluate if you should continue on the feature (does it need just a bit more work) or if its something to come back to in the next cycle.
Just like you say. If something takes longer than expected in the sprint, the retro is the time to call it out, review what happened that made the ticket take longer than expected and share your learnings with the team so everyone is aware of that particular aspect and knows to look out for it next time (maybe it was waiting on another team that blocked you, an unseen complexity, a changing requirement etc).
