Who says South India does not have Gatimaan. It is called Vaigai Express. - Thamizh Maran

The number of failures is not really that different, sir. Most of the sheds maintain their locomotives quite rigorously, particularly the passenger locos. There are differences, but it's not like a particular shed's locomotive being incapable of handling large distances. The disparity isn't that much, and considering that GZB has been the premium shed for 3 phasers for a long time, it is safe to say that they are not that incompetent compared to others.
Here is some data based on the Punctuality loss reports available on e-locos between Jan 2016 and July 2017. I've filtered out the unrelated ones like wheel slip due to rain, non-loco related reasons etc, but there are still a few...
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number of cases where the loco's failure was not related to it's maintenance, so the numbers are only a good approximation (particularly GZB's has more unrelated data that I could not filter out due to the large number). The data is arranged as
(Shed - Number of failures - Number of locos that failed ( accounting for locos that failed multiple times in the period - Shed holding)
GZB - 127 - 70 - 93
LGD - 32 - 24 - 54
RPM - 38 - 28 - 51
HWH - 25 - 18 - 37
TKD - 14 - 12 - 39
Though this seems to indicate that GZB is the worst, that would be a wrong conclusion. While LGD, RPM, HWH show much lesser number of failures ( roughly 50% of their locos have failed in this time), all the failures are very localized. Almost all of RPM's failures are in SR, LGD mostly in SCR, CR and a few in NCR, HWH mostly on ER, NCR ad ECR. However, GZB, despite having almost 75% of it's locos failig in this time, has a much wider coverage. In fact, they cover all of the electrified territory in IR except SCR and SR. On an average they cover much more mileage than the other sheds and just like ED WAP4's earlier, they have very intensive link schedules, not to mention the huge delays on NCR and ECR. All this means that GZB requires a slightly more intensive maintenance schedules than the others.
TKD might look like the best, but again, the work loads for these sheds are quite different and this is not truly indicative of any general trend.
The particular case of GZB link being swapped with an LGD link is most probably just due to some operational issue and it would be rather unfair and inaccurate to use it to generalize the performance of any of the loco sheds.
Sorry for the long post. :)