Makuhita should be High IMHO. The traded Makit grows really fast in RSE, and the fighting typing really helps against Magneton and Slaking, who are two of the most challenging gym Pokemon midgame, and later on he really helps against Sydney and Glacia. Bulk Up is very nice on it.
Also, not being able to hit some types (which isn't completely right as Makuhita has KNOCK OFF... yeah I know, I know) doesn't make a Pokemon worthless in tier listings. Bulbasaur is Top in RBY, yet it struggles to hit those ghosts and poisons. Makuhita is a quickly growing Pokemon whose only STAB is of great utility on your playthroughs, and his only weakness is that speed stat, which is indeed quite a problem. If it's not outspeeding though, it might as well use Vital Throw as it's got nothing to lose. Otherwise, you still have Arm Thrust and could use Rock Smash instead for guaranteed 40 BP before that stupidly late Brick Break TM.
Slakoth could be higher than Low, really. Its bases get good when it evolves into Vigoroth as early as L18 and from there it can fights for itself very well. As Slaking, its performance only gets better, I would argue - you just switch him out after defeating something. With colossal attack power, it can OHKO plenty of enemies with just Slash, and by giving him any of Thunderbolt/Ice Beam/Shadow Ball you give him a chance to contribute to your endgame owning as well. Its special attack is about as good as Starmie's after all.