TL has a marine-marauder-medivac-mine guide, highlights:
Do not hesitate to lift up all units into medivacs and speed boost back to safety if the Zerg starts to gain a favorable position in battle. The goal of this 11:30 timing is do as much 'free' damage as possible to the Zerg. The objective is too kill creep tumors. Use medivacs and mines to ensure that you do not lose any units.
You will be focusing much less on pushing and much more on dropping (and scouting) when the Zerg goes for an infestor style. Use small groups of marines to push out and kill tumors at the 11:30, 1/1 stim timing, but be ready to flee at a moments notice. Eight marines and one medivac is a great group to do this with. Keep your army active on the map but not on creep. On creep you are very vulnerable to infestors that just out of vision. Be wary of moving up mid-map ramps as they are another location that infestors can abuse a clumped up army due to vision created by the high ground mechanic. Each time you see his army, back off and send a medivac drop into one of his bases.
it's less that BL infestor isn't as good and more that mass infestors can no longer hold off all terran pushes pre-broodlords. go watch a game from slayers yugioh where he would turtle on 3 bases and get a hive at 11 minutes and make only infestors and spines and still win because nothing terran has can beat spine/infestor.
BL infestor is still very strong as a ball (though ravens do hurt this) because the projectile fungal is great when you're sieging them.
well its not like you ever needed brood lords to defend against a drop and corruptors arent that slow.
definitely mostly what bsball said, you cant get infestors by 8 mins or w.e and not need to make another unit til your spire is done. pretty sure its still a really powerful composition, you just cant take too much damage on the way there. zerg still so tilty at air battles vT. anytime it looks like you're winning as T, theres a solid 20 corruptors in production at a time
does pdd work against corruptors? seeker missile is good, but it seems so easy to avoid now. if they over make ravens you can prob kamikaze your targeted corruptor into their air ball also. wouldnt exactly call it a hard counter unless microing out of absurd splash is too much to ask for