I've dabbled a bit in LW, MW & SW DXing myself over the years. The big problem over the last 20 years or so has been the increasing amount of man-made interference that was already at excessive levels, mostly from cheap Chinese made electronics that pretty much crap on every first-world regulation regarding causing harmful interference to other electronics but where local regulators (like Ofcom in the UK) have done sweet FA to try and address. I've built my own tuned loop aerials/antennas for long wave & medium wave reception (as opposed to the untuned loops by deeptho) as well as the "mini-whip" based on the work of Dutch amateur PA0RDT and both work very well when man-made interference is not that big of an issue - when such interference is an issue, the directional properties of a loop aerial/antenna can be helpful, but even in some very difficult conditions it can be pretty much impossible to overcome - that's why many still involved in the hobby get mobile and go out listening in local parks, fields etc. well away from (mostly) interference caused by mains AC powered devices.
But as for what's on the bands themselves, the blunt truth is that very few people are still listening to broadcasts on LW & MW these days (with some very odd exceptions), partly because of interference (both the man-made mentioned above as well as other transmitters interfering co-channel & adjacent channel) and partly because of sound quality. In the latter case, most modern audiences in the western world don't want a muffled, mono station** to listen to music if they can help it - it's still tolerable for speech based stations, but those transmissions are also in the process of getting wound down as the costs of broadcasting on multiple platforms bite into costs. Recent data in the UK seems to suggest that stations switching off their MW transmissions to be available only on DAB have not seen any significant difference in their audience figures according to the quarterly RAJAR publications, so it's an easy cut to make where you don't appear to lose any listeners, especially as the cost per listener for AM broadcasts is now higher than all other terrestrial platforms.
Finally WRT the three TXs on 198 kHz - in theory, synchronised networks (as they are often referred to) if done correctly, there should be no interference by receiving more than one TX of the same programme on the same frequency but this is very difficult to do. In practice, even with the best of technical efforts there will be "mush zones" where two or more signals on the same frequency of the same programme will come to the receiver at very slightly different times giving an echo effect if the difference is very small, but if the time gap is significant (for example, the programme it the transmitter sites is not properly synchronised to go out at the exact same time) this can range from the sound being very muffled right up to as if someone is just repeating what they've already said about 0.1-1 seconds later.
This is why the BBC Radio 4 LW network has a few low powered MW fillers in places where two of the LW transmitters can be received with similar strengths to overcome this problem. There are similar synchronised networks in place for BBC Radio 5 Live & TalkSport, but they have an advantage of having two high-powered MW frequencies each meaning that the distances between TXs on the same frequency can be further apart with another TX on the other frequency used on another TX between the other two, solving much of the "mush zone" issues although some still exist. As a result during daytime, reception is fine in most cases except well outside the service areas of the transmitters, but at night it is still important to make sure that TXs on the same frequencies are well synchronised, otherwise co-channel reception from another TX in the chain can ruin reception even in an otherwise strong (groundwave) signal location.
