After testing it in a 24 player server in casual mode, I can vouch that it is indeed not fun with 24 players in a casual setting. Defense has a frustratingly good advantage over both points.
On first, defense has a height/dropdown advantage that's protected by long, tall, and narrow chokes. Even if offense manages to clear them out once, the point takes an eternity to cap, which gives defense ample time to get back to it several times and still have the advantage. Last point is a giant uphill struggle. Defense can confidently extend themselves all the way to the attacker's spawn because they always have the high ground.
Also looked like you tinkered with spawntimes. Please keep them reasonably in line with the standard for that gamemode, only making significant differences as a last resort for balancing.