If you're going to compare Ravagers to MSU reavers solely as an anti-tank option, then you have to compare 2 rounds of ravager shooting to 1 round of reaver attacks, since it takes at least 1 round for reavers to position for rear armour.
And when you factor in all of the positioning, potential jinking(thus losing shooting effectiveness), the possibility of not being able to get good positioning due to area denial, and all the other problems that can arise for a heat lance reaver trying to get a look at the rear armour of a vehicle, I don't think there is any way you could convince me that MSU reavers with 1 heat lance each are going to be better than ravagers with 6 dark lance shots each(before reavers would get a shot). Also, the CC attacks from reavers hammer of wrath attacks don't automatically hit rear armour, just in case you're unaware.
I just realized you're probably new. Don't feel bad, a lot of players spend years playing the game under such false pretenses.
Basically, the argument for MSU reavers as your primary source of anti-tank isn't that they're BETTER anti-tank than ravagers. They aren't. But they ARE a better unit overall, with far more versatility than a ravager. They're a danger to a wider array of targets, but against vehicles, don't kid yourself into thinking they're better. If you KNOW you're going to face a ton of vehicles, you're better off with the ravagers. If you're building an "all comers" list and have no idea what you're going to face, MSU reavers might just fit the bill, depending on the rest of your list.
As for the rest of your list idea, it sounds like you may think wracks from the scalpel squadrons may be able to charge on the turn they arrive. They can't. No units can assault when they come in from reserve/deep strike.
Independent characters also can't join units of monstrous creatures like Talos. The dark artisan is an exception to that rule.
Also, wyches suck.