Legacy's winglet shearing hydraulic/electric lines in the 738's horizontal stabilizer.
That wouldn’t bring a 737 down because it has manual reversion of the flight controls.
Looking at the damage to the EMB and the way the 737 crashed (upside down with the gear out) maybe the EMB winglet sliced through just forward of the AFT pressure bulkhead causing an explosive decompression. The mass flow of air may have then caused extensive damage to the tailsection similar to the JAL123 accident. Dropping the gear may have been an attempt to regain control.
If the 737 had lost pitch control due to damage to the tail, it would presume it still had roll control. As mentioned, the 737 does NOT need hydraulic fluid to remain controllable. With the majority of the tail missing, it’s doubtful whether the flight crew could control the aircraft with roll and thrust alone.
This is obviously just pure guesswork on my behalf and I hope the investigators find and release the cause ASAP so we can debate rather than speculate.
Condolences to all involved.