Want strategies for seiging a planet

[Silent Sorrow]

Hi, all. After a long hiatus not playing the game I've just recently started up a TDM against the AI. What are your strategies for laying seige to a planet? I mean in the sense of being able to invade with ground troops.

I find that by mid to late game the AI has formidable ground batteries (literally dozens of heavy mount weapons) on its large planets that will chew through fleets of ships in seconds, often without my fleet being able to do any real damage, let alone land troops.

In the past I've had to come up with exotic strats like building large ships packed with armour and shields to serve as a screen that leads a fleet to a planet. They soak up the damage, getting pummeled into oblivion and that MAYBE gives my other ships a chance to pound the planet and erase the defences. But as you can imagine, when there are dozens of planets like these this takes ages. I usually then just get bored and use the above tactics but instead drop a plague bomb and let the planet die that way. Not too fun, though. (The AI has no clue about med labs, oddly enough.)

So is there anything I'm missing about how to take on these extremely heavily defended planets?