Actually, I think that 30% of the worlds' population is going to heaven is way high.
While 30% is a reasonable number of people that call themselves Christian, in actuality, a vast majority of those are 'head knowledge' Christians, but are not Christians that are truly born again believers. Even Jesus stated that few would truly be saved:
Matthew 7:13-14 (KJV)
13 Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat:
14 Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.
Additionally, there are numerous references to 'the remnant' throughout the Bible that indicates a small portion. I would interpret that to be something more in the neighborhood of 3-5%. While growing up in the '50s and '60s, I recall my mother did a lot of sewing and always had various fragments and remnants of material left from making a dress or whatever. If they were large enough, she'd make a small pillow for the couch, or even just a hot pad or two out of them then give them away. So I'd expect scriptural use of 'remnant' of people to be something in that range - (all KJV)
Isiah1:9 Except the LORD of hosts had left unto us a very small remnant, we should have been as Sodom, and we should have been like unto Gomorrah.
Isiah 46:3 Hearken unto me, O house of Jacob, and all the remnant of the house of Israel, which are borne by me from the belly, which are carried from the womb:
Jeremiah 23:3 And I will gather the remnant of my flock out of all countries whither I have driven them, and will bring them again to their folds; and they shall be fruitful and increase.
Romans 9:27 Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:
Revevlation 12:17 And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ.
So, how big is a 'remnant' in your mind?