This is an interesting thread, not because I use TrentBarton very often (in fact, never), but because it shows how localised bus use often is, and how those seeking a "one size fits all" option for buses may come unstuck.
Many of the issues being experienced now in TrentBartonLand, by the sounds of it, are those that have been affecting many other companies for years - not just during and since Covid, but over a much longer term, although there is no doubt that Covid has exacerbated things. That's not to say that Trent's users should just 'suck it up', but if it is affecting a company generally considered one of the better ones, imagine how things are at those companies held in far lesser regard. Even a 'good' employer can suffer if a 'better' employer is in the same area, as appears to be suggested upthread with the businesses at and around East Midlands Airport.
It's not just a driver and passenger shortage, but engineering issues as well. There is no doubt that engineering supply chains continue to be quite badly affected, certainly anything containing parts 'made in China' still seems to be suffering negative effects. A significant number of vehicles of one type may have a greater effect than a more varied fleet, especially as Trent seem to favour large depots, rather than having many smaller depots where one might be able to borrow a part in stock at another.
You cannot report directly to the Traffic Commissioners (TC). You can try the company, then BusUsersUK, then the Traffic Commissioner, or via the local authority. However, even if you succeed, as I understand it the TC's aren't keen on hammering bus companies for this sort of thing at the moment: they know if they do one, they'll have to call half of the operators in the country to a public inquiry in fairness, if they cut licenses or fine operators it will only have a negative effect. Likewise as I understand it, a company just has to show they are taking mitigating measures to solve the situation - detailing the driver training currently ongoing and past service cuts are likely to be considered acceptable attempts.
More generally though - with all the talk of Alex Hornby, could it not be more likely that the retirement (assuming it took place) of Jeff Counsell earlier this year have something to do with it, even if just whilst the new person (himself a long term Trent employee) finds his feet?