I tried that too; it works, and even a couple of wyverns survive, but with a more well-thought-out approach, not like in extreme online games.

The 3-13 stats of the Tazar are a very significant difference compared to the 2-1 stats of the Grindan, which is why I wrote that... I meant taking the castle on the map at 121-122 with a purchased growth (without hiding units), especially since you have 4 units loaded. Usually, at 121-122, only 2 stacks are loaded, and there are too many gnolls for a standard army... or a dragon arrives, or a couple of hidden units appear.
Undoubtedly, it was a good exchange, as 4 angels are more effective than the army you lost, but from the point of view of meat for the Fortress Battle, it wasn't a very good choice... the only justification is that you were going all-in.
5 wyverns = 350 hit points, 9 basilisks = 360 hit points, 50 gnolls = 300 hit points, and the rest add up to another 250 hit points... in total, you got 4 angels with 800 hit points, but you lost an army worth 1250 hit points (one and a half times more).
If your opponent relies more on magic, this exchange is not beneficial.
Now, imagine that the stats are slightly lower, and the army is not fully loaded and is slightly smaller in number... how much would you lose, or would you win outright?