I will try to keep a look out on this when I next play the Krynn series. I just don't recall this.My knight went from level 1 to 2 with the same THAC0 (17) and from 2 to 3 his THAC0 shot up to 15. Ranger and Fighter went through 17 > 16 > 15 > 14 with each level.That is not evident on my copy. My Knight and my Fighters all have the same THAC0, except when Clerics of Kiri-Jolith and elves (+1 to-hit with longswords) were involved.I noticed that while Fighters and Rangers have the more usual, gradual THAC0 progression, Knights seem to get a larger THAC0 bonus but only ever other level. That means that they'll lag behind THAC0. Later on when you have more magical gear it will be less of an issue, but at the start it does make things slightly rougher.That is a bit weird. A F/C or R/C should have a worse progression than a Knight of the Crown. In that setup, the Knights should be hitting as consistently as a F/C or R/C. Remember, though, that Knights are tanks, with an extra HD and the best AC in the game. They are designed that way.
But yes, you don't get many Cleric attack spells in the Krynn series. Clerics are there for Hold Person and as a healbot, mainly, which is why you can do without Clerics after the first game since the Fix command is a thing.
The AD&D Cavalier worked exactly like that, no thac0 advancement in 2nd level, then -2 thac0 at level 3, and a -1/level from then onwards. I believe the Knights are a variant of the Cavalier.