There are already a lot of difference between each class.
1)How are they the same? Summoners have a pet and are dot based. Name me another class that has a lot of dots and a pet.
BLM have a unique mana management system and does the most aoe damage among the other classes. That in itself is a huge difference.
MNK has extremely strict positional requirements with it's own combo system (the stances). It's main dps priority is maintaining greased lightning, which requires monk to constantly be in melee. Name another class that has to do that.
2) WAR and PLD are already very different. Having more HP and having a shield are two very different forms of mitigation. More hp is useful for fights with more magic damage because shields don't matter there. Shields are better when there is more physical damage because of the constant extra mitigation. One does more aoe aggro the other does better single target aggro.
3) SCH and WHM heal the same way? What game are you playing? The fact that SCH is proactive healing compared to the reactive WHM makes a ton of difference. Not to mention SCH has a pet with a choice to give more buffs or more healing.
4) The relic system requires a lot of grind. Not everyone has it. To reach it, there needs to be a step-by-step improvement. Before people can get the best one, they are free to use crafting gear. That's what crafting gear is used for. Progression till one can get better gear through a very huge grind system. It is the best only at the end and while reaching that end state, you are more than welcome to use crafted gear.
5) It is obvious why end game raiding gear is the best. What motivation would there be to do raids if one can easily obtain the best gear from crafting? Again, you can use gear from crafting first while raiding before you get those actual drops to replace them.
Sorry to say this but you are blatantly ignoring the differences and only pointing out similarities.