Judging from the ensuing explosion there was still fuel left over.
Stopping a first stage rocket traveling back to an ocean going barge from supersonic speeds with substantial lateral velocity is hard, no matter what engine is performing its suicide burn while coordinating with RCS thrusters for attitude keeping.
Wouldn't it have a thrust to weight ratio well above 1 all the time?
The ratio will be highest just as it's about to run out of fuel. About 160 to 1?
They're also limited in how much they can control the throttle on it.
Even at minimum throttle, it's not possible for it to hover.
Here's another try:
> When near fuel exhaustion, the Merlin engine has a thrust to weight ratio above 1.
The rocket will always have a thrust to weight ratio well above 1.
What does that have to do with the comment you're replying to? The Falcon 9 has 9 engines. The combined thrust of all of them has to be greater than the weight of the fully loaded rocket. That doesn't mean a single engine will always have more thrust than the weight of the entire rocket.
There is a tremendous amount of variables to consider, and the analysis of how to take each into account is non trivial -- if you don't measure some variable precisely enough it might make the whole system less stable, the solution might get worse due to increased computational load, the conditioning might degrade, etc.
So with the number of controls they have and the predictive models available, I'm sure they're actually scrambling to refine their systems right now.