This is not really consistent with your later remarks about the demands of cycling.

Team Sky comment for example about prep. for Tour Down Under:
'Body mass losses incurred during the race will be calculated and riders will consume 150% of the fluid lost through sweating in the hours post-race. Fluid intake will be achieved via a mix of recovery drinks, electrolyte drinks and fruit smoothies.'

With a 300W threshold, you're a strong rider, so, at these outputs, you must sweat a fair bit in hot weather. Unless you are careful with your diet and monitor your water weight, you may well run low on electrolytes.

fwiw, I'm on a low sodium diet, and find 1-2 tabs/day help me recover better and quicker. Low body sodium means the body doesn't store enough water and blood volume decreasing, leading to raised heart beat and an increased breathing rate. My daily records show a good correlation between adequate hydration and lower heart rates during exercise. [and yes, too much sodium isn't great for you either!]

TL;DR? YMMV, but I find these and other electrolyte tabs with salt help in hot weather (former international runner, keen cyclist).

There are zero calories in this, and zero calories in water. You would weigh a bit more from having a higher water balance in your body, but that's not anything to worry about. However, doing some activity would be a good way of losing weight (almost as good as diet).

This would obviously work. However, it involves carrying two tubs of salt, a box of tabs, a spoon, and a sachet or bottle of flavouring around with you, and a couple of minutes stirring. These are quite significant downsides if you're stopping at a water station halfway through an ultramarathon, or trying to minimize your weight on a long cycle.