Base load power cannot provide predictable rates because it provides a fixed amount of power that the market then bids on. If there's too much demand rates go up arbitrarily high. If there's too little rates go to zero.
Dispatchable power is the only sort of power that provides 24x7 power with predictable rates. If there's more demand, you produce more power (at the same cost). If there's less, you produce less so you can sell what you do produce at the same cost.
Base load provides predictable cheap power at night. Which is why heavy industry runs third shift only (only rare industy is this way), and shuts down for maintenance in december (christman lights). Now that wind is cheap they are changing shifts because nobody wants to work third shift if they don't have to.
Nope. What you're describing is an artifact of certain electricity markets work for spot prices. This is artificial, not inevitable. Large industrial customers often bypass those markets and contract directly with producers for fixed rates.
It's the natural way commodities are priced in the market.
Those large industrial customers often also end up selling the electricity in the market. Power companies need multi-decade commitments before they are willing to build anything as capital intensive as a nuclear reactor. In that time, industrial customers need to modernize their factories to keep them competitive. Which is often the time they realize it's more profitable to invest that money somewhere else and wind down the old factories.
Dispatchable power is the only sort of power that provides 24x7 power with predictable rates. If there's more demand, you produce more power (at the same cost). If there's less, you produce less so you can sell what you do produce at the same cost.