First you have your BCs which hit on a 4+ regardless of its armor and shields. 2 SCs give you 6 BCs. 3 SCs give you 9. You seriously wouldn't brace your SDM? Then you'd have the THs (4-6 at the existing setup) ripping out every system inside that ship. You still don't want to BFI?
Look right now, we're down to the question I have asked 3x now. Do the SM REALLY NEED Lances? You still haven't answered that.
Again, D'Art, yes, when you have three times the points values of a ship, you probably will win. And, why would you need a battlefleet? System defenses are more then capable to tearing even three SCs apart.
Let's add other defenses to the crop, since we're upping the points to 480.
1 Space Station
(ringed with)
Platforms: squadroned
2 lance platforms (
2 WB platforms
1 torp platform
(Guarded by)
3 SDMs (squadroned)
(Now I have ordinance and launchbays too. Ho Ho ho.)
D'art, I'm going to assume that you squadroned the SC's, otherwise, I still wouldn't have to brace for impact. However, even added together, their firepower is reduced to 4 abeam. While now I would have to brace, you probably should be firing at the stations and batteries you will have to come in range of to engage them. Since the stations fighters will probably reduce 6 thawks to 4, and you'll want to keep 1 of them on cap anyway against that str 6 torp hit, I'm still not too worried about the thawks.
And, further, last I checked, BCs do not ignore shields, only armor.
And again, what has that got to do with SCs getting lances? Again, the fear of the uprising planet (read the leaders of the uprising) is the SM getting groundside and hunting them down. You cannot easily kill the leaders of the uprising from space. You have to get groundside, look for the rot and tear it out.
If there is an enemy battlefleet upstairs supporting the uprising, what's one ship going to do? So now you believe that one ship supplied with lances will merrily dispatch said fleet when it couldn't do the same with the existing BC setup? Seriously?
Well, using the odds between one SC and 3 SDMs, yes, it would have marginally better odds. With the new simultaneous fire rule, that will improve them against static targets, but it does little to help them against the SDM, which is the vessel they're SUPPOSED to be able to neutralize easily. (Taking 1 cruiser per one monitor is
not easily).
As far as that one goes, the simple and most expedient means is to shoot down the drop pods with ground fire. (which has worked in fluff in the past)
If that is not available: position camouflaged artillery emplacements so that when the space marines attack your (hopefully) empty command post, which always seems to be the first target, you won't be there (though one should always leave behind enough troops to maintain the illusion), but the incoming fire of dozens of artillery batteries and mortar teams will be pre-ranged on that target.
For extra fun, rig the command post itself for remote detonation. Once the second lowest level is penetrated, blow the reactor as the signal for all artillery to open fire.