The only thing that makes a graphic card outdated is lesser VRAM, if you can say that RX580 8gb are no more a good choice for mining what about GTX 1070 and 1080? To me they are in same category, they are old but still works because they have 8GB memory, that's all that matters, if you can pay the bills for power consumption then you are not on a wrong path.
You are wrong, less vram is just a part, high electricity consumption takes over profits faster than Vram, there are old graphic cards with 8gb Vram today but they are bad for crypto mining because of power consumption, you will use the whole profit to pay for electricity bills.