While I agree a 25 Marauder (and my 25 P35) is weak for coyotes I don't think it's good to compare fpe for powder burners to airguns. Airguns are more like pistols. Higher fpe means bigger diameter projectiles moving much slower than PB rifles. The formula for fpe squares the velocity making it terribly important. I use it all the time too but I think you need to be comparing similar projectiles with a similar range of velocity for it to make sense. The PB rule-of-thumb is 1000 fpe for deer, for instance, and almost no air rifle is this powerful. But several states permit air rifles at less than 300 fpe. But the air rifle will be a 357 or larger to get to that energy. Most PB deer rifles are 30 caliber or less. The PB has to expand to make a similar size hole which takes energy. They are just different. Not better and worse, just different.
My opinion is that an airgun for coyotes should be at least a more powerful 25 caliber and preferably a 30 caliber or bigger. As with any gun an expert who is very careful with placement can get the job done with less but I think it is wise to have some margin for non-optimum placement.