Yes, basically black holes growing speed is limited since when they eat they push away the surrounding matter so there isn't enough time. There are also no black holes in between normal size and super massive, both nearby or far away (in the past because of the speed of light)
There is the possibility that black holes larger than the usual stellar size black holes could have formed early on
https://en.wikipedia.org/wiki/Direct_collapse_black_hole
but the gap between those and supermassive black holes is huge and it is not so probable that 100 or 1000 of those would merge in the time available.
Blowtorch theory requires trillions of them
Where does it say it REQUIRES trillions? The way it reads to me, it's just associating the number of SMBHs to the number of galaxies we observe and postulates that number as a trillion, which I don't think is unreasonable given the sheer volume we see in the observable universe alone.
I was merely relaying the content of the article, I was not doubting it.