The LionChief + locos have apparently been a big hit. Hence some explanation for the price increase, no doubt. They were a bargain, now less so. Still, a full featured command, semi-scale diesel for less than $250 which has it's own remote is unique in the hobby (just got a NYC RS3 from Charles Ro for $245). These are effectively command control locos that you don't need to buy Legacy, TMCC or DCS to operate. They come with the remote as mentioned above.
These are somewhat apples to oranges comparisons. A set is cheaper than a separate sale loco on a per piece basis. You can get an inexpensive LionChief Thomas set for half or less the price of other sets, as you know. So Lionel has some inexpensive Lion Chief sets, as well as separate sale locos. These are simple, toy-like locos in the case of Thomas and companions.
Williams is conventional only so there is no option for handing the remote to anyone, anytime, anywhere.
MTH sets are designed for use with DCS, ultimately. If you want to operate two MTH locos on the same loop you need to invest in DCS, another $300 or so.
As a comparison, to operate two LionChief + locos independently on your display loop, you'd need to invest $500 for two diesels or $700 for two steamers. You could buy two MTH sets for that price range, probably closer to the middle of the range than the lower end. But to have independent control of the two locos, you'd still need to have an extra DCS remote, or the entire DCS system (if you don't already have a TIU), so figure on another $150 to get that second remote that comes with the LionChief + loco as standard. And if you don't have DCS, figure on $300 to get that in place, as well as the second remote. For $700 you can have two LionChief + locos and their remotes. If you don't have DCS, you're looking at $600-700 or so for two full RailKing sets plus $300 for DCS and $150 for a second remote to get the exact same capabilities (with the track and rolling stock as a bonus). If you already have DCS, you're looking at $750-850 for the sets and the extra remote. Pretty much a wash, but you get to keep the track and rolling stock 
.
So apples to oranges it seems to me. Different approaches, neither clearly superior. Just different.
