The main reason that you may have long days is the huge distances involved in touring the far West. I have come across people that stay in Flagstaff, to see the Grand Canyon ! That's the equivalence of staying in Bristol, to see Central London. They take hours to get there, stay for about an hour, and then drive back ! Las Vegas is over 250 miles from LA and even farther from San Francisco.
These American coach holidays are rather like trying to see Lands End, John O'Groats, Edinburg, London, Stratford on Avon and Stonehenge, all in the same week. I think that they try to take in too much.
I have travelled extensively in the Far West, but always driving myself. I am not sure I would want to be cooped up in a coach with strangers for so long.
And driving in in California and Arizona can be great fun.
Some friends of mine were on a Golden Triangle type trip a few years ago, and someone died on the coach. But they were so far away from anywhere, that the man's wife had to sit beside her dead husband for about 8 hours.
But the scenery will be marvelous, so it won't seem so bad perhaps.