No, they definitely brute forced it with the 290X. 95C die temps under load were considered "normal and by design". They did beat the OG Titan with it though, hence the release of the 780Ti shortly thereafter.
The stock cooling was bad no doubt but perf per watt wasnt actually much different in uber mode vs stock which shows it had overclocking headroom that was not even pushing it beyond the efficient part of the power curve.
If it was then the 390x would not have been even possible as a sku, since *that* was actually the 290x pushed passed the normal efficiency curve.