It strikes me as high too, but it's possible that he needed more than a 200A 240V main panel to meet code for his very large solar panel system. In the US (I don't know about Canada where the house is) there is a 120% rule, which limits the amount of electricity that the solar panel is allowed to feed into the panel: https://unboundsolar.com/blog/electrical-panel-requirements-....
The idea is that you don't want more energy in the panel than the panel is designed to handle. Practically (if I understand it right) this means that the breaker for the solar panels is limited to 20% of the panel rating.
A 200A 240V panel would limit you to a 40A 240V breaker, which (according to the link above) means a maximum of 7.6kW of backfeed solar.
In the article, he says he has a 11.6kW solar array, which would require (if I'm calculating right) at least a 60A 240V breaker (maybe plus some required overcapacity?). Since this isn't allowed on a 200A panel, he may have needed to bump up to the next largest size of 400A unless he wanted to go smaller on the solar array. So while it sounds like overkill, it's possible there is more reason for it than just a desire to heat his wife's outdoor pool in the winter.
I investigated solar and generation requires appropriately sized circuits and capacity, even if the direction is the opposite.
so 100A panel + 100A of solar requires a 200A panel
A few other things that require high-amp service - on demand electric water heating, and electric car charging (and we're moving towards multiple vehicles).
It's also worth mentioning that by far the largest cost of an electrical circuit is the labor, so sizing for 100A, 200A and 400A is not 1x, 2x, 4x. upgrading later is a huge cost.
The idea is that you don't want more energy in the panel than the panel is designed to handle. Practically (if I understand it right) this means that the breaker for the solar panels is limited to 20% of the panel rating. A 200A 240V panel would limit you to a 40A 240V breaker, which (according to the link above) means a maximum of 7.6kW of backfeed solar.
In the article, he says he has a 11.6kW solar array, which would require (if I'm calculating right) at least a 60A 240V breaker (maybe plus some required overcapacity?). Since this isn't allowed on a 200A panel, he may have needed to bump up to the next largest size of 400A unless he wanted to go smaller on the solar array. So while it sounds like overkill, it's possible there is more reason for it than just a desire to heat his wife's outdoor pool in the winter.