Escalation is the cost people forget
An escalated request is paid twice: once on the cheap model that could not handle it, once on the flagship that could. That is the honest cost of routing and it is included here.
It is still usually a large net win, because the price gap between tiers is commonly twenty to one while escalation rates are in single digits.
The break-even rate
Above a certain escalation rate, routing stops paying and you should send everything to the flagship. The calculator reports that threshold for your prices.
If your measured rate is close to it, the fix is usually a better router — a confidence signal, or a cheap classifier deciding the tier — rather than abandoning the idea.