Contrary to popular belief, TA didn't really bring sweeping economic changes to the table.  The income function is still the same, and the tourism function is, I believe, increased.  However, there's less morale on your HW, as well as less morale from trade goods if you don't use a Terran or Minor tech tree, in addition to more morale holes in specific tech trees.

The reason TA's economy is harder is because everything costs more maintenance, and gives less output.  But the income dynamics haven't changed, and an all-economy strategy is still viable; particularly when paired with Neutral and Thalan or Korx tech trees, since the rush buy purchase reduction didn't actually work in DL or DA.  Furthermore, techs cost more in TA, with inflation thresholds that kick in earlier, and peak higher, reducing the pace of your civilization's research.

TA's reduced planet count does mean somewhat less overall income, as does the change to the Mind Control Center, but the unique mining modules from the new tech trees as well as the extra tiles granted by the Weather Control Zenith and Biosphere Modulator tend to more or less balance this out overall.

Technically speaking, TA's economy is actually better than DA's-but only in the late game; the early game is quite a bit harder, due to the above.

Now if you're talking about the focus nerf, it was reduced from 25% efficiency to 20% efficiency (exception: industrial to industrial is still 50%), while you still lose 25% of the original production type.  It makes it harder, sure, but it doesn't make it useless by any stretch of the imagination.  Just don't bother with it before adding buildings to a new colony-14 research/industry loses you 4 (3.5) of the initial type, but only gives you 2 (2.8) of the focused type.

Actually, the rush buy cost can be as high as about 14x the build cost, for high end ships (without extra shrinkers).  The non-lease rush buy formula is trunc(build cost^1.1)*6, whereas the lease options are ^1.1*4, ^1.1*2+50, and ^1.1+50, with differing lease costs as well, but that's the basic idea.

The fastest way to get things done is with research and rush buying, but that doesn't mean it's always the best, especially if you can't afford it.  Even with the lesser complexity of DA, it's difficult (but by no means impossible) to set it up fast enough for it to be competitive with actually building things.

For some reason, I never caught that, but as that has no effect on non-lease rush buys, it doesn't seem to be accurate with regards to the description.  So I for one am glad it was changed.

Good eye.

I submitted a bug report to that effect...over two years ago.  But even with Thalan/Korx and Neutral you need another 50%.  I suspect they're not worried about it, because the only source of it in an unmodded game is a single post-colonization, pre-ethics event, out of 32 possible, where only one event window will show per turn, and the maximum value is 50.  This means that either you need a 50 straight away, or you need the event to fire twice-at least.

Granted, 100% isn't necessary; I'm pretty sure we'd all be satisfied with, say, a 95% reduction.