> The core of this question is: Quantitatively, what are typical values
> for $Q_{eng}$  realized in state-of-the-art fusion reactors?  

As far as I know, there are no fusion reactors with the downstream infrastructure that actually generate power. This means any quoted figures for $Q_{\text{eng}}$ would be a theoretical estimate. The other issue is that both $Q_{\text{eng}}$ and $Q_{\text{econ}}$ are highly scale-dependent. For example, if the heat produced is used to power a steam turbine generator, the efficiency of the steam generator can vary from as little as $10\%$ for a very small unit to as much as $40\%$ for a huge industrial steam turbine generator. The scale makes a big difference to the viability, and all the current fusion reactors are at the small end of the scale. Actually, being able to take the heat and convert it into electrical power will take further research and engineering ingenuity, and I don't think we have even started that stage of the development process yet. Most fusion reactors are a batch process. To be useful, they will probably have to design a linear continuous process. I do not know if it is feasible, but ideally, we would take the fuel and compress and heat it in something like a straightened-out version of the LHC and eventually let the plasma impinge on a water-cooled target to absorb the heat to create steam for the turbines. I imagine such a device would have to be at least several, if not dozens, of kilometers long.  

As mentioned above, $Q_{\text{econ}}$ is also highly scale-sensitive. For an automated plant, a large plant does not take much more personnel to run it than a small plant, so the labour cost per $\text{KW}$ output is diminished, and there are other savings that always come with scaling up to industrial scales. Exceeding $Q_{\text{econ}}$ is not as important as exceeding $Q_{\text{eng}}$ because a power plant that produces electricity on a windless night can fill the gap when solar and wind power are not producing. If a fusion power plant can do that job safely without polluting the environment, then it is useful even if it is running at an economic loss. Its main competition would be lithium battery banks, large gravity batteries and nuclear power stations.