I just did 2 Defender mode games.
first one :
60 minutes, 2x diff 7, 3 planets, one entry wormhole, Bonus ships: shieldbearers, viral shredders, bulletproof fighters
It felt dull. Totally. Every 3 minutes 20s of action and then more waiting.
The only problem I had was scrapping the shredders on time so I don't get a brownout.
15k kills, 9k scrapped shredders. 1000% kill to loss ratio.
Oh, and venturing out into ai territory, antagonizing but not killing EMP guardians is a very bad idea.
Most of the time I spent thinking about what I could do with all my resources. Turns out reactor efficiency does not fall below 10% so at the end I had 181 reactors MK II, enabling me to power all unlocked towers, all ships I could build + about 2500 shredders total.
second one:
60 minutes, 2x diff7, 13 or 18 planets, don't remeber if it was a 15 or 20 planet mark, I left 2 free, one entry wormhole. bonus ships: many.
first wave: 3600 ships. doable.
second wave: 7600 ships, including ~1500 Bombers, 100 spire tractor platforms and many starships. No chance.
Is it by design that ship caps don't scale with the number of planets?
Next thing I will try is a 15 minute version.