It isn't, but there's a difference between a train that isn't spotlessly clean and one that is pretty embarrassingly dirty. The condition of the unit on the inside, reliability/frequency of service etc. is far more important, but it's a matter of principle. If I'm going to pay 307% the fare to travel 125% of the distance (Stratford-Shenfield vs. Limehouse-Upminster on Oyster PAYG single), I'd expect a fairly professional looking service. As said, the 321s aren't
as bad, but even they are far from clean.
On the SWT debate, it's not the colour scheme - they're all comparatively spotless, even on the mostly plain white livery of the 444s, and further they're also always spotless on the inside, even the old 455s.
WRT reliability, from memory the 360s across the various fleets score highly now, just not when they were first introduced, which has been true of most EMU classes, even back in the BREL days - I'm told the 321s were troublesome at first launch. There's a commonly held opinion that all newer units are generally unreliable, the 'new trains being returned for modifications due to defect' press articles don't help matters, but statistically, after the first couple of years I don't think that's often true, except perhaps in the case of the Junipers, and even they seem to be doing reasonably well now?
That aside, more on topic, the issues raised with the traction package on the 321s at present I can relate to, the anti-slip is particularly tedious in wet weather, such that from Stratford it can take as far as Seven Kings to reach 80mph - that's what, about 4 miles? Any EMU is going to suffer on wet rails, especially one with only 4 powered axles per 4-car set, but modern units seem to recover faster (I've also heard a 321 anti-slip fail to respond quickly enough on one or two occasions and thus heard the traction motors achieve what must be a speed in excess of the 100mph maximum - they've never reached that pitch in service, that can't help reliability either).
From a personal perspective out of pure coincidence I've experienced one failure each of the 315s, 321s and 360s. The 315 was failed on departure at Shenfield heading back to Brentwood (no reason stated, but they did lower the pantograph in the platform which seemed unusual). The 321 was also declared a failure at SNF but heading towards Braintree (again, no reason specified). The 360 was heading towards London somewhere around Great Bentley/Weeley, and one of the door sounders never stopped after the door closed, and presumably didn't report its closure - a staff member appeared shortly afterwards and locked it out of use - they then told us the unit would be terminating at Colchester to go into the depot - seems a bit excessive for having one door out of use on a Sunday, but there you go!
This comes after having used the GE franchise casually perhaps on average a dozen times a year each way for a bit over 10 years, then every day in one direction only for 2 years (school run Chelmsford-Brentwood), sparsely for 5 years (away in York, but for the city's university, not its railway heritage
), and for a period when I worked near Liverpool Street, every day both ways for about 6 months, since then perhaps once a week in one direction only on average, as I primarily use c2c to Upminster for the punctuality, reduced price (£2.70 each way from Bermondsey at peak time for a 20 mile near-central london commute is a bargain tbh), somewhat reduced overcrowding and more comfortable (e.g. air conditioned) rolling stock.
Over all that time I must have covered, hazarding a complete guess maybe 20,000 miles on the route, so to experience three unit failures? not sure how that works out statistically.
Been using c2c daily for about 15 months thus far and not been on a failed unit yet, been disrupted by one once or twice in that time, and I must have racked up about 10,000 miles on that line so far.