Jungle Valley is one of the hardest map bosses, period. WILDLY overtuned for a mid-tier map, always has been, I have no idea why GGG has never fixed this.
Pledge (I love this staff btw) and Doon Cuebiyari have level 30 gem effects built into the item. 28 is the highest you can take any *actual* gem, items are exempt from this limit (in those two examples).
Level 30 spell echo/iron will just have more power than the lower level versions. Echo adds even more cast speed, iron will even more damage.
Same goes for Firestorm, a level 23 version just does more damage than level 19. Scaling gem level with +gems mods and/or Empower is a major way that spells are scaled into lategame, and one of the few reasons Staff weapons are used at all by casters (for anyone who isn't stacking +gems and Empower, a 1H + shield is probably going to be better unless they need a unique staff effect).