I can tell you have taken this seriously and with deep thoughts.

I am a family med doctor in Utah county for background info.

Here is my best attempt for answering this post.

Vaccine causing more spread:
Virus's multiply in their hosts. We will say that whether they have symptoms or not, a person who has the virus is infected and contagious. While it is true that a person without symptoms is more likely to be in the community, the trouble is that usually for 2 days prior to symptoms, every infected person will be spreading the virus. For those who have had the vaccine, their immune system will be able to fight off the infection faster and therefore less likely to have symptoms, but also less likely to have viral shedding after the first few days. So, the biggest impact for slowing the spread is to lower the amount of people who are infected.

Delta variant less/more dangerous:
I think the scientific way to phrase this question is to ask what is the mortality (death rate). I calculated what the mortality in Utah since Sept 12 through yesterday to be about 0.5% mortality (5 people die resulting from COVID infection for every 1000 confirmed infected people). That mortality rate has not really changed since the beginning of the pandemic. Utah has been very good at testing, likely better than almost any other state and therefore probably best suited to evaluate mortality rate. I think the sharp rise in the numbers we are seeing is because the delta variant is more contagious. The other point is to look at where people are having the worst time with COVID right now, and it is in the states that have not done as well with vaccines (Alabama, Mississippi, Idaho)

I'm sorry to hear about your cousin. I don't have a good answer for you, and we probably will never get to know for sure if is was the vaccine or would have happened anyway. I don't think it is unreasonable to be highly suspicious that it was from the vaccine, however it may not help you decide whether you should get the vaccine or not.

Over the past 40 days in Utah we are around the 50% mark for people fully vaccinated and during this time there have been 52,239 new confirmed COVID cases, only 7,627 among people vaccinated; 270 deaths, 61 of which are among people fully vaccinated. If the vaccines were not working, the numbers should be about 50:50, but the numbers are about 85:15 (vaccinated:unvaccinated). Currently the estimates show about 55% of the people in the US have been vaccinated.

It is always possible that the numbers are being made up or tweaked by the government. I have skepticism like most reasonable people. But as I work in healthcare, I see real people who have had their lives destroyed or ended because of COVID infections. This morning, my wife's 46 year old cousin died from COVID leaving his now widowed wife and 4 kids, a patient of mine yesterday told me about her brother-in-law who is in his 40s died last week leaving his wife and 6 kids. These people were generally healthy, but unvaccinated. Now their wives have to not only try to make their way through life without a husband, but also try to properly grieve their loss while trying to reconcile the guilt of "what if" their family had decided to get vaccinated.

I don't pretend to be the smartest doctor, but I encourage you as one cougar fan to another to get the vaccine. Good luck friend!