Yes, the almost auto-kill that assault boats did to Escorts really made it hard for people to ever want to take them.
I mean... 2 abs would kill an ork onslaught 90.2% of the time? when 6wbs would kill the same escort what? at best 15% of the time. And 2 lances 1/4 of the time. Way too absurd of a difference for the weapons effectiveness.
Some things can be more effective than others, but that much just made people who liked escorts run into any of the fleets with assault boats and explode.
It actually very much killed the idea of ever running any escort heavy list, as it would just get blown up if anyone had assault boats.
Now with the 4+ thing, it makes them just a little more effective than bombers at killing escorts.
Lets look at the Sword with the 4+ H&R rule, vs 2+:
2+ 2 Assault boats: 66% chance of death
4+ 2 Assault boats: 43.75% chance of death
Actually not all that different. Even though it seems like a lot. Effectively 1/3 less effective. Now for the 2 bombers:
They have a 36% chance of killing the same sword. Still the assault boats are quite a bit better at murder, 1.2x as good in fact.
However there is a point where bombers become slightly better than abs at killing escorts, and that is against ones with low armor and low turret strength, like the ork onslaught, but iirc. this isn't that big of a difference still.
The advantages of assault boats are that they have a longer range than bombers, by a whole 10cm (in most fleets) and they can stop a ship from shooting back sooner than bombers. However they are quite unreliable, as you were hoping for anything but port, and that is what you got.