How to win with a “weak” Knight?

I didn't quite understand. It's quite difficult for the Warlock not to control Dragon City. The Sorceress and Knight usually get there faster. But the Warlock needs to build dragons in 2 weeks and then spend another 10 turns moving them to Dragon City. It's unlikely to create a chain; there isn't enough money to have 7-8 heroes.

Warlocks with gargoyles and magic could control the approaches to Dragon City, with the task of weakening the Knight's army if he tries to go there.

And taking a Sorceress while playing as a Knight... as I understand it, you wouldn't play as a Knight, but as a Sorceress. Yes, but to get a Dragon Lord, you need a strong hero with decent stats and build Phoenixes. And that also takes until day 15 and beyond.

As I understand it, the discussion started with an offline map playthrough, and then gradually shifted to discussing the specifics of online play.
Regarding playing as a Knight offline: everything depends on the specifics of the map generation, and there's nothing you can do about it – the Knight has some common elements, such as building Paladins in the early game, but it's unlikely that all of them can be discussed. The most effective way to figure out how to play as a Knight in Good vs Evil would probably be to hold a speedrunning tournament on this map, with the participants generating their own save files (similar to the KIs on the Portal) and the condition that the starting hero is a Knight. Provided that at least 5-6 strong players participate.
My comments were more about online play at 160%. Considering the number of outposts along the way from the Warlock to Dragon City, the magic level will be at least 5 by the time he gets there, and considering the Knight's army, a couple of mages with 1+1+1+1+1 gargoyles, even with ranged attacks, can weaken the Knight's army so much that capturing Dragon City becomes problematic – while the other heroes calmly gather resources for the dragons: 7-8 heroes – the more heroes, the more resources they will gather. Moreover, the Knight has nothing to counter this tactic. The possibility of capturing a Sorceress was also mentioned in the second week as an option for further development if capturing Dragon City is complicated by any circumstances. Phoenixes can easily deal with the roaming mages, but I wouldn't use them to storm Dragon City: they won't be very useful there; they can bring much more benefit by roaming the map.