I think all were affected in different ways tbh. I don't think there is a worst year. They all lost important years of their lives and were impacted in different ways. For some the academic impact is more obvious and for others the social.
I've got a current year 12, 10 and 7.
Year 12 missed out on so much of the foundation years before the GCSE course and then other stuff compounded that like all the teacher strikes. Then they also had more of the COVID exam allowances in my terms of advance knowledge of topics, formula sheets etc taken away.
My year 10 like yours missed that important transitional time.
My year 7 lost those years where they really start to learn social skills and conflict resolution. The behaviour of his cohort is deplorable and it really affects him. His confidence going in to secondary isn not at all what I expected it to be, he's stressed and dispirited.
Mine are also at one of the worst affected schools by RAAC so still missing practical science. My year 7 has had online learning, a rota for coming in to main site combined with online learning, being taught off site and now in temp accommodation. He's had a constant parade of different teachers. My year 10 has missed a whole year of practical science yet will be graded alongside kids who had no disruption and their performance will be measured according to the same criteria. My year 12 has also experienced disruption and had only recently regained access to the specialist classrooms required for their practical subjects.
There are, and will always be, things that impact their education. I feel far more answer towards RAAC than I do COVID tbh. At least with COVID all kids in all schools were being treated equally.