Some heroes are good, some suck, most are okay.
Almost all content can be completed with a Level 17 Forge ( 100% mana potion), two rainbow 4* 3.60 teams and one GOOD rainbow 4* 4.70 team ( total of 15x 4* heroes)
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I advise getting training camps to 1x 20, 3x 11 then raising a Forge to 17, since a Legendary training ( RT 20 ) produces a 4* hero every 10 days on average and Extra low cost training ( RT11 ) is the most hero XP per recruit, requires no ingredients ( and little food ) BUT is very very slow so running multiple really helps.
Getting a second training camp to 19 lets you do Legendary and Extra fast ( RT19) at the same time.