I don't agree that gascans are "ineffectual" They are different from starter pitchers, as explained below but can certainly make power throws that will be difficult for batters to hit.

When Ian says that "There isn’t a lead big enough." he seems to be saying that the Sox will lose their 2 run lead against the Angels as soon as the "gascans/power pitchers" come on for them

https://www.sportspundit.com/baseball/terms/3389-gascan
A gascan pertains to a pitcher who runs in bunches, [...] he will fill a fire with gas. [...] It is similar to a power pitcher because these guys throw tough and are often called fireballers or flamethrowers. Today, in the 90s, a strong power pitcher can throw even 100 miles per hour. They might not be as moving in the air, but it is challenging for the batters to “catch them” before they get into the captors.

https://www.sportspundit.com/baseball/terms/3376-fireballer
A fireballer in baseball is defined as a pitcher that throws high-speed balls over 95 miles an hour. It is a great technique to beat the opponent and make it difficult for the batter to hit the ball.

[...] manipulates the grip at the point of release to achieve variety and thereby improve the defensive ball strategy. Differences in grip allow the seam to “catch” in the air differently, altering the ball’s trajectory and making it more difficult for the batter to strike.
==============================
So this is when the relief pitcher can make a difference...
https://www.reddit.com/r/mlb/comments/16gqmix/can_someone_pl...
A reliever doesn't need as many pitches because he typically only pitches one inning and thus doesn't even see the whole lineup once, let alone three times. It's easier to keep a third of the lineup guessing than it is to keep the whole lineup guessing three times through. [...].

A starter also needs endurance, while a reliever needs quick recovery. A starter needs to be able to throw 90+ pitches in one day, but then he gets 4-5 days off to recover from it. A reliever might only throw 10 pitches in a day, but he needs to be able to throw ten pitches the next day too, and maybe the day after that too before getting a night or two off.

Because starters need to go all day, they need to pace themselves. This means few starters are fireballers, they need to get guys out with trickery. Starters are typically breaking ball specialists and more cerebral. But relievers are often heat specialists, using brute force to get guys out.
This is because a reliever is only planning to throw nine pitches a night, so he can pour everything he has into those ten pitches. A starter can't come out throwing 103 because they'll destroy their arms before getting to 90 pitches.

https://www.reddit.com/r/mlb/comments/16gqmix/can_someone_pl...
Relievers also need nerves of steel. Relievers come in when it's higher pressure -- it's late in the game, so there's less time to make up the difference if a reliever pitches poorly. This weighs on players' minds. Starters can be like "we have all night for the bats to make it up if I can't get out of a jam", where relievers coming in up one run in the bottom of the ninth instead have "if I give up one it's going to extras and if I give up two it's game over right then and there".

--------------------------------------------------
Note added at 6 days (2023-11-29 11:16:14 GMT) Post-grading
--------------------------------------------------

glad to have helped