They were perfectly decent trains when built, they've continued to do a reliable job on one of the toughest TOCs in the country
I think some people (conveniently?) forget how different the railway was back then
AFAICS it had been a decade since the last main line was electrified the last section of the ECML to Edinburgh, there was no prospect of any major expansions (the enormous WCRM project had only wired a short bit of line from Stoke to Crewe, there was the Heathrow Express with significant private funding, but apart from that...). Plus electrification had such a bad reputation that GNER were suggesting taking the wires down permanently because they were more trouble than they were worth
Operation Princess had the name because the Cross Country services had previously functioned with hand me down trains, whatever various main lines to London had grown out of (90s for key WCML services freed up 87s for shorter routes, meaning there were 86s spare that could go to Cross Country, ECML HSTs freed up by electrification)
In the same era, FGW was ordering five coach 180s for London to Cardiff, MML ordered two coach 170s for London to Nottingham/Derby (inc services to Barnsley, Burton, Matlock etc), the Transpennine service was in the hands of 158s
All this feels primitive now but it was only a few years earlier that BR was running 156s on some relatively long distance routes (Norwich-Liverpool), and before that it was 150s on e.g. Scarborough - Liverpool
So the Voyagers were a big step forward, a fairly guaranteed standard of service (compared to mixture of 47s/86s/158s and HSTs), a constant service week/year round, rather that the nationalized days when the flight of longer trains seemed designed around the leisure traffic heading south west on the morning and home in the afternoon
One huge difference with XC is that all of these other TOCs were allowed to expand further. The two coach 170s from St Pancras were replaced by three coach examples, then those by four coach 222s. FGW gained surplus HSTs, allowing them to run routes like Cardiff which cascaded 180s to places like Oxford, freeing up 166s for other corridors.
XC were never allowed to expand though. IAIUI the initial plans had been for subsequent Voyager carriages, but that wasn't permitted. The ambitious Project Thor (building more Voyager carriages, with bi -mode capability) didn't get the green light either.
In comparison, look at the Transpennine route that I mentioned earlier. It had gone from a trains like 150s to 158s. AFAICR the stand alone TPE franchise planned for 60x four coach 185s but this was watered down to 51x three coach examples, plus 9x two coach 170s. However, TPE has strong regional government support, both Labour and Cameron governments seemed understanding/sensitive regarding it's needs (or at least the demands of mancunian politicians). It gained three fleets of brand new trains, plus got to retain the full fleet of 185s, which meant quite a capacity increase. And there's more new trains on the way for TPE, politicians will listen to the likes of Burnham
Nobody seems to be successfully beating the drum for XC though. It's too big to easily tweak, too thinly spread for any regional authority to treat as a priority, the Voyagers are second fiddle on pretty much every significant bit of track it runs over (other than New Street to Derby line)
The franchise feels like it's been in a coma for at least fifteen years, no government has dared grasp the nettle
So most of the Voyager hate feels a little misplaced (and I say that as someone who's ridden them from Aberdeen to Truro, and used to commute daily on them)
The main problems are:
1. Various opportunities to extend them or expand the fleet size were missed (too late now, of course)
2. The franchise has been ignored since about 2011 (i.e. when the plans should have been formulated for what happened at the end of Arriva's operation ended in 2016, rather than short term extension followed by short term extension)
3. In hindsight XC shouldn't have had 125mph trains in the first place. Controversial but the short sections of 125mph running weren't worth the loss of capacity caused by crumple zones and the fact that only 125mph stock could keep up with Voyager paths meant XC were never able to bid for the various 100mph trains that subsequently came to the second hand market
3. Given this, any sensible railway would have focused any other 125mph DMUs on XC d and when they were freed up. But instead we are seeing younger six coach 222s going to an Open Access Stirling service with various five coach 180s trundling around Yorkshire on a different OAO, taking an hour and a half to get from Doncaster to Bradford, plus some of the five coach 221s freed up at Avanti either still in storage or with Grand Central. Those routes shouldn't take priority over the XC core IMHO
The future for Voyagers? It's probably got to the stage where I'd keep them on their existing routes but throw the full fleet of 222s into the mix and things will be better. Plus, ideally, reduce the strain on XC's diesel fleet by focusing electrified trains on electrified routes, which I've discussed before