Whilst I can't speak for the actual delay caused during your trip. I would say you got off very lightly considering you were traveling during one of the busiest and expensive times of the year which is the August summer holidays, on a Bank holiday weekend and in a pandemic. There were reports of travelers waiting up to 3 hours as well recently. So while you have a right to be upset at the processing time it may be worth trying to plan better in the future. You need to remember UK immigration is a service to ensure those coming into the country are not a risk (safety and security) to nationals by checking properly those coming in the credentials they have and not abusing the system while they find more and more sophisticated ways to do so.