If someone has advanced Stage 4 lung cancer and gets run over by a bus and killed, what killed them? The bus accident or cancer? A little dramatic but it serves to illustrate a point. What is written into death certificates as significant co-morbidties has to be something that made a significant contribution to the actual cause of death.
Medics don’t just write in causes of death and significant co-morbidities contributing to cause of death without thinking (least most don’t). If covid is on the death cert then it is likely to have made a significant contribution to the cause of death.
Also, a large percentage of people over a certain age are going to have one and often two co-morbidities. If someone has hypertension and/or ischaemic heart disease (15-20% of UK population over age 65) and gets infected with Sars-Cov-2 they may be less able to compensate for that further insult but the insult is covid.