Well Phil your calculations on tankless vs tank are not quite accurate.
You also forgot that Tanks unless flushed regularly loose efficiency
every year. I just had a tank replaced in a bldg it had over One Foot
of scale- crap in it after 17 yrs. Now that reduced efficiency apx 20
-25 % . Also buildup scale Hard scale cant be avoided in tanks. Tanks
only go down in efficiency , Tankless don't have these problems , they
don't scale. they remain at their rated as long as the burner is clean.
and last 2 to 3 x longer.

For figures on savings you are wrong. I know people that say the same
as me 25- 50 % in costs of operation. saving 15 - 40 a month.
There are allot of people with tankless , they are how you should base
your opinions. Real world everyday use. Not guesstimates.