I echo this response. And I’m quite interested about the statement about how you kept the planning but just removed the sprint goal posts. If you were continually over planning and underdelivering in the sprint cadence, then you would be likely to do the same in any other approach. My recommendation would be to understand the root cause of the continual overcommitment.
BTW, individuals are usually optimistic about their estimates. Nobody plans for issues. Perhaps doing a root cause analysis or 5-why exercise would help. Maybe you are doing top down estimation for road map planning, but not doing a deep dive or bottom up estimation for sprint planning. Maybe there is a step missing in the design approach that is leading to too much interpretation by the development team about what the requirement is actually asking for? Could it be related to a refocus on acceptance criteria? Maybe planning for workflows and wireframes? Could be lots of reasons.
Also keep in mind that many don’t have the option to forego long term planning. I have been on many projects that must have a road map of capabilities they intend to deliver. This is needed for budgeting and resource planning. There might also be other systems that are waiting for you to deliver a specific capability. Signed business deals might require a commitment by a certain date. Therefor understanding why there is an overcommitment is important.