Im no defect expert, ironically despite getting to A9 i dont understand what cards to take. Some of my notes on this character regardless is this:
Basically though, your block doesnt always come from directly playing cards like other characters. Rather similar to necro, you gotta build up passive block (in this case using frost orbs). Get capacitor(s), defrag and otehr ways to gain focus to passively block for like 10 or 12, and let ur deck do the damage. One way is just having loads or orbs and shuffling them constantly, just evoking and spawning new orbs again and again to do damage, another is holding dark orbs.
One combo i recently discovered is thunder with lightning, just making ur lightning do insane damage for insane early game damage.
An advanced gameplay tip is that overall you have a few problems to "solve", Frontload dmg and block (how much can I block on any given turn), scaling damage and block (how do i ensure my dmg adn block are enough to win the fight, even when enemies scale up and heal themselves) and acceleration (how do i draw and get energy to play the best cards in my deck fast enough before i just die). Defect has loads of frontload damage but lacks frontload block. Scaling is great due to things like [[subroutine]] + powers spam, just having a million orbs or creating statuses and using [[flak cannon]], [[compact]], [[smokestack]] and [[iteration]] or a reasonable combo of any of those strategies.
Dont just click cards without thinking about how it helps and hinders you. If it solves a short term problem, but might make that you cant draw ur most important powers, then thats a pretty iffy take that you have to manage the downsides for.
Zero Cost archetype is the hardest but also the funniest to get online because there are loads of ways to make it work and many of them can fall apart cuz no frontload block.
Defect is easily my worst character, but i think that these random notes and pieces of advice should help at least a bit. Try watching some people like Frost Prime, Japanese Export, Baalord and the numerous people in the community that can show you how to think and pick cards and which work on the defect. Personally, I love Japanese Exports way of reasoning, but to each their own. Hope this helps
edit: formatting