I think the data from the UK, at least in terms of the vaccine preventing serious illness and death, is about as conclusive as it gets.
To clarify, I understand the point you are making on the hospitalization numbers. If 100% of people are vaccinated, of course 100% of hopsitalized people are going to be vaccinated. There's plenty of anti-vax people spreading misinformation on hospitalization numbers that clearly don't understand how the math works (or those that are doing it for darker reasons). I think the latest report out of the UK is 40% of hospitalized patients are vaccinated, which on the surface would seem about what to expect given that the oldest population, even if vaccinated, would still be the age group with the highest percentage of people requiring hospitalization. However I saw that number being used throughout Twitter yesterday saying it's proof that the vaccines don't do anything, which as we both know is absurd.
My concern out of the Israel data is that for those over 20 years of age, the % of cases lines up with the % vaccinated. I.E., in the 40-49 age range, if 80% of people are vaccinated, 80% of cases have the past couple weeks have been in vaccinated people. I would expect at least some statistical difference there. Perhaps that's skewed by parents catching it from unvaccinated children, thus skewing the numbers there? Not sure, but it is something worth watching. It is encouraging that despite their recent increase, it's still a very small "wave" there up to this point. Which if the vaccine is still highly effective against severe illness in delta, which it certainly seems to be, then we really don't care much about cases in vaccinated people at all. The only concern then would be them being able to spread it to unvaccinated people.