Understandable, but it was good enough for a 10k WR in 1984.
As I understand it, being that it's a faster pace than the standard LT run, you accumulate lactic acid quicker (after all, a 45s 400 causes tons of lactic acid) and the ≈45s jog recovery isn't close to full rest, so every rep you're getting a little more lactic build-up and the 100m jog is really what becomes more difficult. It's like a 5k-8k 2:1 fartlek...
The key seems to be knowing how one's body reacts. If the OP just doesn't like tempos, he/she might just need to suck it up in order to improve. Or OP might need to break up the tempo, do cruise intervals, do Igloi-type high-rep low-rest workouts, or eliminate tempos altogether.