It is not unusual for a thermal breaker to hold 200?ated current for 10 seconds, so that is plenty of time to frap the SCR.
There is an old saying the transistor (or SCR) will blow to protect the fuse in the circuit.
If you want to protect the SCR, a high-speed fuse is a possibility. That is why the spec sheet gives an i^2t value. Pick a fuse that limits the let-though current to well less than that value.
From your data sheet, the 25A SCR has an I^2t maximum of 510 A^2s.
A 25A 388-series glass fuse from Littlefuse won't do the job. It has an average melt time of 3717 A^2t:
But a 20A 505-series ceramic fuse has an average melt time of 145A^2s, so that would be a better choice:
There are many fuse types. By browsing the fuse manufacturers' web sites, you may find the optimum selection (re cost, availability, physical size, melt curves, etc.).
It is normal practice not to load a fuse beyond 80?f rated current. Fuses are rated in open air. In an enclosure, it is customary to derate the fuse to 80?regarding long-term steady-state current). The manufacturers' have more design data.
Regarding the 16A, I don't see that specified anywhere.
A thermal breaker's rating of say 20A is 20A RMS.
There are also breakers that have a magnetic trip that will trip the device. The trip range typically is somewhere between 5x and 15x rated current. They are more expensive. But they can take 1/2 or more cycles to trip, and not limit the current while tripping, so an SCR can still be damaged. A fuse is a more reliable means.