Blake was genuinely satisfied with the second method of isolation that he created using the darkness element barrier.
He had thought about using the darkness element barrier first as his first-choice method of isolation but decided that he should try out another method first, which was the dark earth dome.
However, the reason why he chose the darkness element barrier as the second prototype instead of the first one was because of how weak it was compared to the dark earth dome.
The darkness barrier could be made to be a strong barrier if it were to be supplied with constant nether, and it could even rival the toughness of a dark earth dome if it was supplied with enough nether.
However, with just a simple train of thought coming from that statement, the darkness barrier was able to be as tough as the dark earth dome, but it would consume a huge amount of nether.