I always like challenging and more varied scenarios in the game, but agree with @Throne_of_Rats that dodging should always be possible.
I find even boss walls rather inelegant and would prefer it if bosses were not triggered spawns but roaming enemies (why not more than 1 on higher difficulty levels) but for that are also dodgeable.
Or you could “convert” the loot rats and give them a small bell instead of a bag, when they escape they trigger a boss (or other support troops), just a kind of alerter.
Furthermore, this topic was also discussed HERE before.