'Bits Falling Off' is I believe also airline slang, where it is often abbreviated to BFOs. I have a small box for BFOs on my layout.
For steam models, in general, I find that Hornby's are much more flimsy than Bachmann's with bits much more prone to fall off or break off. They also tend to be harder to get apart, although the Bachmann Austerity is a challenge until you know how to do it - hopefully not having broken something along the way. On the whole, diesel models are easier to get apart, but Hornby's are usually much more awkward than other makes. Some years back there was a whole thread on this forum's predecessor dedicated to how to get a Bachmann Mark I apart, so they are not immune.
Wires between engine and tender are a bit of a nuisance but a plus point for Hornby here is that their engines have tender pick-up as well as engine, whereas Bachmann's don't usually, although they still have the wires. DCC is the way forward for much of the market, so those like me who are still analogue just have to live with it I suppose. At least there seems to have been some move away from just doing a particular model with DCC sound and not the more basic version, although there are still exceptions.
In my experience, Bachmann locos tend to be more reliable and more durable than Hornby ones, with the latter suffering far too much from the dreaded mazak rot. split gears and wheels going out of quarter. My first Austerity is approaching its 20th birthday and still gives good service. Some of my Hornby steam models are nearly as old and still work. The problems are often with the newer models it seems.
Pulling power isn't a problem for the vast majority of modellers. My engines will happily pull 8-9' long freights or 9 car trains, which is all they need to do. I have a layout without any gradients (at least in theory). Modern-day diesel models are usually in a different league though, and are often able to shift 20 or more carriages, and possibly many more than that.
Hornby detailing parts are generally finer and more fiddly than Bachmann ones but often fit better.
I have spent much of today bringing my eight new Bachmann Mark 2f coaches into service. None of the ETH detailing bits fits without chipping off the paint from the spigots because whoever designed them probably forgot that the orange paint adds a few microns and means they won't go into the holes. Once in, they really help to finish off the models, which at around £46 a go for the ones without lighting are in my view good value as they are the first air-con Mark 2s that actually look the part after three previous poor efforts by Airfix, Lima and Hornby over the past 42 years (yes, it really is that long since the first Airfix ones appeared). As I don't fit the brake hoses, I now have lots of spares. Similarly with tail lamps, as each carriage comes with no fewer than four, although two are the more modern type that are out of period for me. The bodies are easy to get off on the 2f stock, by the way. One irritant with current Bachmann coaching stock is that the metal inside the bogies, which gives very good bearings, and that is designed for lighting, means that one wheel is linked electrically to the other one on the same side of each bogie. This is an absolute pain on an analogue layout as it means bogies bridge section breaks. Hence, I have had to take apart 16 bogies to alter them to break that link. I had to do the same with the Porthole and Thompson stock too.
Apart from being bulky, I think most RTR loco packaging is better than it used to be as we no longer have expanded polystyrene so I think models are easier to get out of packaging than they used to be. Once detailing parts have been fitted, one problem is that engines won't always fit back in their boxes without hacking off bits of packaging.
In spite of a few irritants and areas where manufacturers could do better, I think we are in a very good place right now in terms of overall quality and range of models. I type this with 10203, D601 and D836 sitting next to me with paint drying from a bout of weathering. All are superb models with little, if anything to complain about. They can all shift a long train too, as 10203 demonstrated round Little Bytham last year. Not that long ago, who would have thought that we would have such high-quality RTR models of these three types, and many others?