Like any business model, it CAN be. But there are things to keep in mind
#1 They've reduced commissions massively over the years, and there's no reason to think that trend won't continue. They may pull the plug entirely. They have zero loyalty to affiliates and you mean absolutely nothing to them.
#2 They can and will ban you for any reason they like, you likely won't be able to speak to anyone and almost nobody gets their affiliate account reinstated. Their TOS are vague and extensive, so you're likely to fall short somewhere. They hold earnings (each months earnings get held for 2-3 months from memory). And they will keep it all if they ban you.
So if you want to invest the time and energy building up a business on a foundation that is essentially a tightrope, you can do it, but it's worth considering backup options in case Amazon screws you over at a moments notice. So if you're building Amazon affiliate sites, make sure you can monetise them some other way, because if they're built 100% with Amazon in mind, then you're completely at their mercy.