You start off by disagreeing with the assertion that Frigg and Isarnia are grossly unequal and state that the two are “not as far apart as you think.” Then you go on to compare the two:
And as you seem to lay it out, by my measure, that’s roughly two categories to two categories, with one, according to you, being a wash. All of which sure makes it seem like you think they’re awful close in usefulness.
However, your analysis is grossly misleading. You admit that Frigg is better in raids. Then you pretend as if they’re equally useful on map, quest, and event stages—they are not. The only PVE stages you’d take Isarnia over Frigg are in the Riddles of Wonderland (where green damage is reflected). Just about everywhere else where there is a balance of colored tiles, you’d be smarter to take Frigg. You rank Isarnia better against titans than Frigg, but this isn’t true either. Isarnia is better against red titans, but Frigg is better against blues. (You wouldn’t want to take either against any other colored titan.) So titans is actually a wash. Lastly, you list “rush wars and tournaments” and “regular wars and tournaments,” suggesting at least graphically that they’re both of equal weight. They’re not. Rush tournaments are 1/3 of the overall tournaments. So Isarnia will be useful there 1/3 of the time as compared to Frigg. Rush wars are 1/6 of the overall wars. In attack boosted, field aid, arrow attack, equalizer, and horde wars, Frigg is indisputably better than Isarnia.
Their value in raids, wars, tournaments, and map stages all grossly tilt in Frigg’s favor. The only place they’re roughly equal is against titans. (Though even against titans, Frigg is particularly unique, being the only defense-down green hero, whereas there are other blues who can approach Isarnia’s usefulness, albeit not as well.)
Now all of this is not to say that I think they should be equal, or equally useful—I’d just like to see a bit more equity. It’d be nice if heroes felt useful at least somewhere meaningful in the game.
The game’s power creep has skewed the game’s balance, and these newer heroes and features are making parts of the game feel obsolete, as the OP rightly pointed out.