1) Why restrict something that the developers came up with? Where is the element of randomness?
2) The number of monsters is something we can discuss. I personally believe that +5 monsters of level 7 is a bug, and it has been present since the first Heroes game (those familiar with the first game understand that this bug is more pronounced there).
3) I think it is quite fair to allow purchasing only the bonus that is the base bonus for that unit (2 for all 6th-level monsters and for phoenixes, and 1 for the rest of the 7th-level monsters).
4) The probability of a specific monster's weekly bonus appearing is approximately 1 in 140 (9 castles x 14 types of creatures).
5) I believe that the appearance of a weekly bonus affecting monster growth occurs more often on week 211 than on the 3 preceding weeks (121, 131, 141).
From points 4 and 5, as well as the presence of a large number of weeks that do not bring any bonuses, we can obtain the true probability of a specific monster's weekly bonus appearing, which is many times less than the chance of a level 1 bonus near a castle.
Conclusion: Of two evils, I choose the lesser.
2) I personally don't consider this a bug; in fact, I think the developers planned it this way.
3) Everyone has their own opinion.
4) There are also weeks with rabbits, etc. In fact, this is a theoretical debate; out of boredom, the number of games in which the outcome is decided by a monster's weekly bonus is no more than 1 in 100. Various bonuses and minimums on week 111 much more often decide the outcome of a game. I'm tired of arguing about this; consider it whatever you want; you can even ban the purchase of 5 extra monsters :D