I can't get over that "Discord has bad reaction speed/is slow argument".
"But he got tagged by Chrysalis". 1:10
You mean THIS scene, where the villain trio were AMPED off the REAL GROGAR's magic. To the extent Cozy Glow turned into a FUCKING ALICORN.
All this really proves is that the Real Grogar was strong as balls, given HIS magic SPLIT THREE WAYS is enough to make any of these three a match for Discord.
Meanwhile you know what else is in this same season?
1:20
Here's Discord not only casually reacting to the attacks of King Sombra (who is at least equal to a non-Daybreaker Princess Celestia) but PHYSICALLY MOVING faster than those attacks.
Not only is he waiting until the very last second to neg each attack, not only does he TURN HIS BACK to talk to the Ponies while still reacting to the attacks without even looking,
Sombra is ONLY able to hit him when Discord basically tells the dude to aim at Fluttershy and INTERCEPTS IT. Taking the hit deliberately.
Straight up admits this by the way.
1:00
And HERE'S how the villain trio fared pre-amp by the way.
But nah "Starlight hit him so he MUST be slow". Yeah let's just ignore the fact Starlight is (at best) = Princess Twilight < Starswirl the Bearded <<<<<<<<<<<<<<<<<< Princess Celestia </= King Sombra and this is still true by EoS.
We can therefore safely conclude that Discord LET STARLIGHT HIT HIM, just like he did with Sombra, because he was trying to make a point. In her case, that she was unstable and not mentally fit to run Twilight's school, he specifically provokes her into hitting him.

Discord is slow my fucking ass.