Isn't that a similar power output to a class 43? Admittedtly there would only be one 93 whereas an IC125 has two 43s, and five mark 4s and a DVT is probably a fair bit heavier than half a HST, but an IC125 can do 125mph and TfW won't need to go above 100mph between Holyhead/Crewe and Newport. With the Welsh Goverment listing electrification to Swansea as a priority 'by 2029' something capable of electric operation to replace the 67s on the mark 4 sets wouldn't go amiss, although I suppose by then the mark 4s wouldn't be too far off retirement anyway and you could bring in a new fleet of bi-mode units to replace them IF you still had something that isn't too new on the rest of the service.
You would indeed have less power than a HST, which aren't exactly known for being quick off the mark.
Bear in mind as well though it's not the speed of the line that's the issue, it's the hills. The Marches line is pretty steeply graded one way or the other pretty much continuously from Sutton Bridge junction in Shrewsbury to St Julian's viaduct in Newport - it's why back in BR days a special batch of 158s were built with extra power specifically for that line.
Class 93s on diesel hauling 5 MKIVs and a DVT would make for a painful journey.
I do agree though that between the advancement in loco technology, and the possibilities for extended electrification, it's certainly possible in the future we'll see Bi-Mode locos. But at the moment, there isn't a Bi-Mode loco powerful enough to keep to time on the Marches and fit British loading gauge
