A scoundrel can get four dots in an action rating (even multiple ratings), but that doesn’t immediately suck the tension out of the game.
First: four dots in an action doesn’t much matter if the position/effect for using that action is dire. “I’m going to try to leap across this chasm by propelling myself with a grenade! Four dots in ‘Wreck!’” “Okay… That’ll be a desperate action with zero effect. Would you get +1 effect from somewhere on this roll?”
Second: the crew’s Tier and the Tier of their opposition still influence the fiction and the position/effect negotiation. A Hound could have four dots in “Hunt,” but if they’re using a T0 rifle and trying to pierce the breastplate of a T6 Imperial Military sergeant… well, their effect is still going to be limited/zero.
Third: scoundrels that have maxed-out action ratings are usually scoundrels that have been in the game for awhile. That probably means they/their crew have made enemies, possibly powerful enemies. In my experience, “season” two or three of a Blades campaign is a good time to lean into NPCs/factions that have a grudge with one or more scoundrels.
If my Cutter has a history of raiding Ministry of Preservation trains, the Ministry is going to eventually strike back, and they won’t strike back on the Cutter’s terms (by, say, sending some toughs to kill her). Instead, they’ll bankrupt the Cutter’s friends, buy up the Cutter’s family estate, and generally use their influence to attack the Cutter where she’s weakest.
TL;DR: Scoundrels with maxed action ratings should be good at that action. But just being good isn’t always enough, especially if a scoundrel is dealing with an unfamiliar situation, high-Tier opposition, or opposition that knows how to get around the scoundrel’s competencies.