Setting-wise, you're sort of right. Deadlands is the "Weird West" of horror and gaslamp fantasy while Boot Hill is a straight-up Western where the campaign setting is literally just the American frontier in the 19th Century.Deadlands is almost the same as Boot Hill, except Deadlands is more ghostly western. Boot Hill for Clint Eastwood
types. My dm called it last weekend since there were only two of us and the other standbys flaked.
I'm not too familiar with Deadlands and I know there were different editions of the original game and official adaptations for other systems like Savage Worlds but Boot Hill was all TSR and had three official editions.
Boot Hill 1E was from 1975 and was one of the very first RPG's ever made alongside the 1974 box set version of D&D, and was more or less a glorified man-to-man wargame for the Wild West and combat was highly lethal and used percentile dice.
Boot Hill 2E came out around 1979 and was more or less the same as 1E with the percentile dice system but there was a bit more of a proper RPG framework to it and also some conversion charts for doing crossovers with AD&D, Metamorphosis Alpha, and Gamma World. The same conversion chart also appeared in the original Dungeon Master's Guide for Boot Hill-D&D crossover games so it must've been a semi-common thing in the 70's and early 80's.
There were also a few extra supplements for the game, namely a DM screen, a set of miniatures, and some campaign modules for Boot Hill 2E in the early 80's.
Boot Hill 3E was released at the start of the 90's, around the same time as AD&D Second Edition and it was a typical late 80's/early 90's RPG. I don't know if it ever got any extra supplements or modules like 2E did. I never played 3E or read it, but I do have all the 2E stuff on PDF and that's what I use.