wrong for 2 reasons.
1) i mentioned gtx 970 because they are not being used for crypto. crypto mined cards are: rx470, rx480, 570, 580, gtx 1060, gtx 1070 are among the most popular. After that it's older generation AMD cards such as the r390. So nothing to worry about used gtx 970, 980 and 980ti.
2) crypto mining is all about efficiency and return on investment. What this means is that any seasoned miner will UNDERVOLT the cards in order to use less electricity and generate less heat and noise. so even if running at max 24/7 they are being run with less voltage, and thus they are actually pretty safe even after years of mining.