[isatty]

Guessing that 0.8x size increase for 1300% speedup was worth the tradeoff but maybe ≥1.5 size increase or more was not (especially considering a 1300%->2000% increase is not going to be user visible for 99% of the packages).

[TJSomething]

It's not 0.8 times size increase, it's a 0.008 times size increase, since the unit is percent. The latter seems pretty marginal to me.