I got that each one was an alternative, but ive always found my rig took care of most of, if not all the fizz in any OD's ive used, unless i didn't want it to. All the OD's ive owned had EQ options on them and i always found the treble knob to do enough of a job without needed more specialised EQ or equipment. None have had speaker sims or dedicated LPF. I do love the Sansamp BDDI and i know that has a cab sim built in, but i use the blend very low, and don’t actual use that for OD.
Totally agree about the PA/DI though, as thats more unclouded when it arrives at the PA and for most a PA will have a lot more top end accentuation. I think ive only used a large PA a handful of times, and that was back when I didn't use dirt at all. I'm quite keen to keep the top end in check anyway, as i play with a pick and dont really like the 'click' i get. I do like an open top end though so the tweeter normally sits in the neutral position.