Having travelled almost exclusively with US-based tour companies, I can't tell you who to avoid, but I can tell you that the larger ones have very firm protocols in place for COVID, including mask-wearing. So in response to your assumptions:
You may be in a large bus but it will be to allow social distancing. You may be required to demonstrate you have up-to-date vaccinations for 2 reasons: (1) to enter the country, and (2) to travel with the provider.
Depending on the provider you may be in value hotels, or 5-star properties, and prices reflect that. Location of a property depends on the tour. In-city may be preferable, but if the country has a high incidence of COVID or other transmissible illness, you will be sleeping outside the city but have transport to the high density areas for scheduled activities.
Oh, and you will need to carry travel insurance to covers costs of your stay if you have to quarantine in place, medical coverage, and coverage for transport home if you can't use your return ticket.
Bottom-line: you pay someone else to handle the details, know specifically which areas are safe to travel in, and provide a high quality set of protocols to prevent COVID from being transmitted (or any other disease that is endemic in that area).
- Rita