Any argument about why you should play sorceries or splash a color in Solidarity is an argument in favor of another deck. I don't think the people making these arguments actually understand why Solidarity is a good deck. If you expect to have to go off turn three, then Solidarity is a bad deck. Almost every other remotely viable combo deck is better at going off turn three. The only reason Solidarity is ever worth playing is because you can wait to go off until you know you need to. It's not being faster or more resilient that really wins Solidarity games; it's being able to wait and force the opponent to actually get a lock or kill in place before you can combo off, and thus giving yourself those extra land drops and card draws that make your other cards better. Disrupt, Merchant Scroll all fail to contribute to this.

Here's the list I've been running lately:

11x Island
4x Scalding Tarn
3x Flooded Strand

4x Brainstorm
4x Opt
4x Impulse
4x Cunning Wish
3x Thirst for Knowledge

3x High Tide
3x Reset
4x Turnabout
3x Meditate
2x Flash of Insight
4x Force of Will
3x Twincast
1x Brain Freeze

SB:
Brain Freeze
Meditate
High Tide
Reset
Twincast
Hibernation
Misdirection
Echoing Truth
Stroke of Genius
Careful Consideration
Rebuild
4x Wipe Away

As per the above, some of the ability to go off very early was sacrificed to make turn 4 as reliable as possible. Hence using Cunning Wish as a tutor, for example. It is simply unbelievably convenient to be able to just Wish for whatever you're missing; having played this for a bit, it actually seems insane to me that the deck ever used to maindeck all 4 High Tides.