The bassrig stuff is modelling the preamp, poweramp, reactive load and cab sim that’s been tuned to match the original cab - it’s going to do one thing but it’s going to do it really really well.
the VTDI is a preamp with a simple cab sim at the end, I don’t know how complex it it is shape wise. Where I’ve seen an electrical examination of the VTDI the character knob is a variable eq curve that can dial in a more driven sound, or dial it out (b15 a like)
It’s a great pedal big “I want a B15 sound in a pedal” investigations don’t often mention the VTDI as an option. I think they sit in different categories, an Ampeg sgt would be a closer alternative- or if you really were after two bass amps on a budget the tonex one would probably do it digitally.
Origin aren’t doing it in digital, are U.K. made and are aiming at a level of “let’s engineer this thing well” where price point and value for money aren’t their primary driver of what they are doing.