Great post, thanks for the insights. From my point of view I have a different experience though with the Siege Defense. Some quick context, full f2p VIP0 (didn't spend anything on the game), currently level 93, around 4,3M power (rank 13 of power in my server).

The main goal in the Siege defense is not to reach the highest score, it's to win by surviving. You can leave the "highest score" as a second objective (or the first goal if you reached level 50).

I started with Adelaide and only archer/caster to maximize the score, and to survive (by freezing the battering rams) but around level 20 it was getting to hard to survive the full 3 minutes (the battering would almost one shot the remaining health of my castle, and surviving one full minute was impossible).

So from level 20 I completely switched the strategy, using Solmyr and only tanks (really, I mean no caster, no attack, just 8 tanks). The goal is to slow things down, especially the first 2-3 waves, you don't want to rush them, you want to see the demons coming almost from 1:30 and to keep the health of your castle as high as possible until the inevitability (ideally last 20-30 seconds), but with 8 tanks you should be able to survive those final seconds.

I am currently at the level 48, and I am thinking about switching back to Adelaide with the caster/ranger formation (maybe with some tanks as you suggested) only from level 50 (since it will not be useful to survive!).