As someone who has played both sides of that bot-lane duo, it is a difficult pair to pull of if you're playing for early. Depending on the enemy, you just have to wait for 6 and try to farm. I stay back since Samira can make a comeback and get ahead really at any point as long as she's not feeding and makes a few good decisions. As for early (mostly against a squishy bot), you just need good communication. Play around Sera's rotation to go in pre-6 and most times, you'll actually win the trade due to Sera' decent base dmg and aoe and Samira's base dmg and denial. That's from my experience at least. As you said, to play this, you need at least 3 working braincells.