I'd be happy to run a QKD in a "mediocre" lance. They're a perfectly fine addition to the highly regarded 55 ton Medium 'Mech trio, except that they weigh 60 tons. Granted, they're one of the poorer Heavy 'Mechs, but if you play them as a typical 55T Medium they're reasonably effective, and fit in nicely with them from a firepower, armor, AND speed perspective. The variant which has the 4xMLs facing forward, and the SRMs facing back, is actually pretty nasty.
The SHD is a generalist, and neither "good" nor "bad" in my opinion, although its firepower is a bit on the weak side against other 'Mechs.
The RFL is likewise effective in roles where it's not fighting other 'Mechs, and is able to provide decent supporting firepower in situations where it's not a primary target for the opposition. Unfortunately, it's slower than the rest of the proposed lance, and will hold them back.
A VL makes a very good anti-vehicle platform, sends infantry running away screaming in terror, and serves as a reasonably effective scout-hunter, but is once again not designed to fight other 'Mechs.
Overall, I'd take that lance in a contract where they're not expected to be facing other 'Mechs, or for general security duties. I would refuse to use it in any kind of "battle line", and make sure that any contracts taken would exempt the unit from such actions at the discretion of the lance leader.
As for the WTH suggestion, yes please. A WTH provides the same long-ranged firepower as a Dervish, and holds the same amount of armor, but at only 40 tons of total mass instead of 55. It's got roughly comparable short-ranged firepower as well: 3 MLs instead of 2 MLs and 2 SRM-2 racks, and both designs need to "bracket fire" the weapons best suited to the range to the target, rather than alpha-striking and overheating. The only significant advantage that the DV gets for its extra 15 tons of mass is one more point of speed. I've fielded WTHs in numerous battles, where they were able to provide reasonably effective fire support until the ammo ran out, and then their 3xML secondary weapons were generally adequate for "cleanup" operations against whatever was left of the opposition. They won't stand up for long against something nearly twice their size, unless it's already been hammered pretty badly, but they're dirt cheap for what they bring to the table.
The comparisons that I often see here are between "typical" units that most forces would field, and the rare "cream of the crop" pieces which only a few units can afford and manage to acquire. The OP's suggestion stacks up at least passably well against the "norm", but would clearly be outmatched by the optimized and specialized forces which most players tend to run. Would I specifically choose these units? No. Would I be willing to use them in roles at least somewhat suited to them? Sure.
