These are usually pretty small spaces. So heating them isn't that much of an problem. And going from 22 to 80 for a few hours a week or day isn't too wasteful.
But a hot tub? There are very, very few bodies of water that you can submerge comfortably in that doesn't end up being a non trivial amount of energy to warm up, much less keep warm.
No, a lot of saunas in Finland are electric heated. But they're still only 3*16A at most (and usually a lot less, but that depends on the size of the sauna). I think mine is ~7kW and still heats the sauna to high temperatures, just takes a bit more time.
I still don't get though, if living in rural area, why not heat the pool with wood. It just has that sensation that electric heater doesn't provide.
There is a common saying when living in areas when using wood for heat -
‘Wood warms you up three times. Once when you cut it, once when you split it, and once when you burn it’.
The amount of manual labor and time required to keep a pool warm from wood is monumental. It will definitely keep a fit man in the prime of his life busy and tired.
It isn’t something to sign up for lightly, especially for someone who may not have that kind of physical strength (or want it spent on heating their pool).
Is this for a wood-construction sauna with a heater warming up rocks that you can steam water off of? That's a lot less mass to warm up, mostly air, and a lot less ongoing energy loss than a big heated pool.
My house has 350A split across two meters because we have a ground source heat pump which has a special electric rate. I don't think we ever actually use that much power.
Where I live we have to pay to the electric grid for the amps on the main breaker. Because the grid has to be able to provide those, needs to be planned accordingly, needs to have the proper diameter cables and transformers, etc. Even if we don't use them. So having 300A "just in case we need it" would be insanely expensive on the monthly bill. This amount of apmeres is more like for a workshop, small industrial or office building
Many utilities will do this based not on the amperage to the house but the peak kw used in a billing cycle - a capacity charge. This helps incentivize reduced peak usage. In your scenario it's strange because you have zero incentive to keep your maximum usage below the breaker amount, other than the per-kwh cost.
I live in the same such country with such rules. They assume rightly that if you request that amperage you will use it and they will plan and bill you to handle it. And yes we then also pay per kWh :)
Why would it be harmful to run at the amperage that I'm buying ? What disincentives do I need?
I also think it's ridiculous, for what it's worth. 400A is a wild amount of electricity for a supposedly high efficiency, modern home.