over the term of the mortgage you nearly always pay less when on a variable rate
This is true UNLESS the banks have mispriced their loan.
The bank gives up the flexibility to vary the interest rate, understandably they charge for that.
The borrower gets certainty over the repayment amount, understandably they pay for that certainty.
While obviously banks cannot fore tell the future, they expect a greater margin on a fixed rate loan, otherwise they would not take on the additional risk.
What has changed since the 90s is that the range of possible future variable rates is no longer symmetrical about the expected rate. If the variable rate today is 2% it might be 6% in 10 years time but is highly unlikely that it will be negative 4%.
Comparison with Tracker Mortgages
The tracker mortgages of the early 2000s were a one way bet, either the future unfolded as the banks expected and the tracker was a good product (for the borrower), a nice variation on a variable mortgage, or, as actually transpired, interest rates increased and the tracker was a great product (for the borrower).
This 20 year fixed rate mortgage has somewhat similar opportunities for borrowers. If variable rates stay the same on average over the next 20 years, borrowers will have paid no more and benefitted from the certainty. If variable rates go higher, or much higher, this product will be a wonderful opportunity for borrowers. If variable rates fall borrowers will lose out (though they will still have the certainty) but there is a limit to this downside, variable rates cannot go negative nor even close to that.