I have seen them on this forum. Very infrequent but they do happen. I have not heard of dGPU problems on the 2015; just the 2014. I haven't seen them on the 2013.
If there's a failure possible, you'll probably see it here.
Yeah some have proven reliable.
But my point is that over the past decade there's been a roughly 50/50 chance of your dGPU machine dying over 4-5 years. No one has 4-5 year old 2020 machines yet. There's an even chance they're going to be unreliable just like half the previous models.
Combine with the higher initial purchase price, and the idea of buying a 15-16" machine "for re-sale" is pretty silly.
If you need the power you need the power - buy it. But don't go spending 1.5-2x the price (for 13 vs 16) for "re-sale" purposes when
- in terms of the money you'll lose - the more you spend the more you are likely to lose, and in percentage terms the 13s tend to hold better percentage of their purchase price anyway
- it may well be worth zero some time after AppleCare runs out due to hardware death. this has proven to be far more likely to happen to the larger machines than the 13s if long term history is a guide.
I'll put more trust in larger machines when apple has had a sustained run of not having them break. Likely after they switch to their own silicon - iPads seem to last forever and the heat issues will likely be a lot less of a problem.