I don't think I understand how the prongs approach works. You would need the other ships (including the center one) to shift into a new prong configuration as the attacked prong falls back. But that doesn't work very well in space because there is no 'friction'---the new prong would need to reverse thrust to slow down making rapid reconfigurations more difficult than you might expect. For the Lie Ren, target selection and target switching is certainly a tricky process, part of why the crews are elite. (Another part is because accuracy is super important at extreme ranges.)
It does seem plausible that fleet maneuvers can significantly reduce the rate of safe fire that the Lie Ren can put out and can cause the damage to be distributed relatively evenly across the fleet. My expectation is that there is a significant learning curve here due to the shift in tactics from a "wall of battle" that characterizes every battle so far to something much more fluid.
CC doctrine prioritizes destroying the enemy's strategic mobility, making jumpships a higher priority target than warships. As a consequence, a jumpship heavy fleet (like the TH) could find itself forced to defend a (relatively) fixed position (the location of the jumpship fleet) against the Lie Ren limiting tactical flexibility.
A simple tactic moving beyond the wall of battle is a sacrifice play: detach a ship or a squad to pursue the Lie Ren while the fleet moves on. The Li Ren might eventually kill off the sacrificial ships, but that gives the other ships a huge head start in going wherever they are going. Alternatively, the Lie Ren could dodge the sacrifice play to pursue the main body of the fleet, but that takes up significant time.
W.r.t. the fighter approach, part of the reason why the Lie Ren is so large is to achieve invulnerability to fighter scale weapons. If we were playing with standard BT rules, that would not work. (On the other hand carrier tactics are overwhelming, so I don't think that's a mistake...)
W.r.t. crews getting exhausted, that seems very plausible. Both sides would be suffering here. I'd estimate the elite side has an edge in combat under equal levels of exhaustion, but at some point rest would certainly be required. If the Lie Ren disengages periodically for rest breaks, combat stretches out over significantly more time than a day.
It must be said though that bad luck or a bad tactical decision could easily destroy the Lie Ren. Jumping into a pirate point where the enemy happens to be, turning left when you should have turned up, misjudging enemy ship speed & location, etc... are all very natural failure modes. How far does it manage to go before a critical mistake is made?
Incidentally, the "easy" counter to the Lie Ren is to just have a slower ship with more LNGs and armor. The FS already halfway does this.
