The rule of 30 may look stern but I believe it's for the best. My grandfather died last summer and while holding a service inside the church was forbidden and large gatherings not encouraged - for funerals, only the presence of the family was officially recommended, - there were many people who showed up to the churchyard. I appreciated their desire to say goodbye and they did try to observe some distancing but it was hard. It was particularly difficult to keep my sister in-law, who had a two month old at the time, sufficiently apart from everyone else. Many times during the service, I wished that she had just stayed home but she insisted on coming. We had an elderly mourner with a heart condition faint due to swelter and emotion.
Overall, I support the forced reduction in numbers and 30 is a decent number even for someone with so many to mourn him as the Duke of Edinburgh. It's good of everyone not so closely related to free up space. We're living in a very particular time.