You cannot compare the two . The 360s are a quality established product . There was a time that the class 360s were one of the most reliable fleets in the country.
Could it be that the servicing and maintenance regime is different from that of the previous operator?
I have to use the Corby service from Wellingborough now, to connect with Inter-City services to the North. I notice that failures of 360s occur pretty much daily; 'problem with the traction equipment' 'problem with the doors' being the usual. On other occasions the service is a single 4 car presumably the result of a failure that's only affected one set (obviously not a problem for the small numbers of passengers conveyed at this point). You can confirm this by looking at RTT.
I haven't noticed a change in the level of cancellations to 360s over the passage of time - it's neither improved nor deteriorated. Some days there's been two circuit workings missing due to these failures.
An interesting contract with the Cl 350's I also use, from Northampton, and failures on them
were very rare, but even these have gone down the hill recently, with, for example, a pair stranding their unfortunate passengers for about 4 hours just South of Northampton recently ('a problem with the brakes'). And a few 'problem with the doors'.
Some of the cl 360 problems must reflect poor maintenance rather than design, I accept - air conditioning / heating not working, the tired seats with different moquette patterns, the dirty carpets, unwashed windows are also symptoms of lack of attention - but the seats, too narrow even for someone with a healthy BMI, are down to design. Curious that both classes 350 and 360 are maintained at the same depot.
Edit; both the 10.10. and the 10.40 Corby - St Pancras cancelled today due to 360 failures.