I don't understand how need for farming planets = not advanced tech/industry?
Plants are not the best place for an advanced civilisation to set up shop. O'Neil showed that back in the 1980s and no one's come up with a better argument than, "But planets look nicer." For a couple of their two-mile-long ships they could build probably enough orbital farms to make earth unnecessary. That's the smarter approach technologically, because lots of little targets are harder to kill than one big target.
The Faey don't see things this way. So they're either run the same as as the Amtrak Federation, or they're not very bright, or a combination of the two.
Is it better to die in a futile fight now
False logic, presupposes the humans *knew* the Faey were serious about fighting. The humans did not know this. (Remember, at this time, Earth's combined land-forces alone is on the order of 10,000,000 soldiers.) From their point of view, it would have been very possible for the Faey to be bluffing.
"Ha! Puny Earthlings! I tell you Zerg, it won't even occur to them that our *snigger* two mile long starship is just a fifty meter tug hidden inside a two-mile long mylar blimp!"
Affecting Earth's tides again wouldn't do the trick. According to our current understanding, gravity manipulation is mandatory for FTL, and that kind of synthetic gravity well is on the order of magnitude for creating an FTL effect anyway. Again, impressive, yes, but not war winning and certainly no justification for surrender.
What about if being "conquored" by these invaders actually makes life better?
If the first chapter bore any relationship to the Faey's behavior to the rest of the story, then maybe. Unfortunately despite the implications in the first chapter than the Faey 'aren't that bad', by Chapter twelve the Faey seem intent on destroying every single human institution on the planet and carrying out intellectual purges against anyone who's got more than a high-school diploma. "After all, they're all going to be farmers, right? And an educated population is a *dangerous* one!"
Since this is the worst case scenario anyway, again, why did the humans surrender?
You can bluff when your opponent thinks you may have a chance of winning, however slim that chance might be. When your opponent is sitting in an interstellar spacecraft out of reach of all of your weapons, you are not in a position to bluff.
Or when you think you have a chance of winning; or when you think your opponent is bluffing/has a chance of loosing. See above comment about Zerg and mylar blimps.
On the contrary, Faey tech is much more advanced.
No, their *science* is more advanced. Technology is how you use that science to solve problems. With advanced science comes more advanced ideas on how to solve them - and the Faey have yet to show this. See Amtrak Federation comment above.
If you had reread the quote there from the prolog the Earth Governments were being just as arrogant as ever
Actually I just did, and they've about as spineless as amoebae. In fact they're as spineless as important people have in stories where The Hero/God-PC/Mary Sue is fated to save the day with his supreme intellect, perfect body, ninja skills, vast psychic powers, and the strange attraction alien women seem to have for him. Now of course that's slightly unfair, but not by much.
they figured they could pull a fast one and come out on top
Which would only be true if they believe (and had reason to believe) that this would be the best tactic, rather than the worst.
all they would lose is some cheep labor
Unless the humans outsmarted them just once. Say, a hidden 10MT mine combined by a stupid Faey general destroys a division of Faey troops. At the least that would be severely embarrassing to House Trillane. Which is the point. You give them a bloody nose in the hopes they'll back off, and if that doesn't work you make them damn well pay for what they take. Whatever form that payment takes.