It totally depends on what you are shooting with and what your target is. Suppose you are in an Ywing, and hit with 1 success and 3 advantages.
Your choices are
1 hit for 7 damage with a critical
2 hits for 7 damage, no critical
If you are shooting a TIE/ln, pick the linked with 2 shots, it takes it out of the fight completely (2 hits at 5 damage after armor).
If you are shooting a YT-2400, I might pick either result. 4 armor reduces damage to 3 points per hit. The YT 2400 has 25 hull, it may be better to crit it to death.
If you are shooting at a Nebulon-B, pick the crit every time. 6 armor reduces your damage to 1 point, vs the Nebs 71 hull. You will take it out by crits far faster.
Now if you regularly hit with 5 or more successes, I might go for linked more often. At that point, armor becomes far less relevant.
This makes some sense and it would be great if crits were a more reliable way to attack larger ships. But don't larger ships have a much better chance of having 1 or in the case of a Nebulon-B multiple engineers so they are much more likely to be able to use actions on mechanics to get rid of the crits and so the crits are not likely to "stack" or stick?
The number of crew that can take an action increases, but so too should the number of crew needed to take that action at all. Twenty engineers on a frigate shouldn't be ten times as effective as two engineers on a light freighter, as they are likely to be spread even thinner than the pair on the smaller ship. However, if every crewman is able to take actions, then bigger crews make ion weapons fairly useless as large ships can shed hundreds of SS per turn. Obviously an extreme example, but I've seen a PC and NPC crew on a Gozanti shedding 4-6 strain per turn and making me wonder why the bad guys (pirates) would even bother with ion weapons.
Even though its not really implied, I could see limiting a ship to one mechanics check a round that represents the combined efforts of a full complement of engineers. Big ships have more SS to represent their ability to take more punishment. Could make it too easy to take out bigger ships though. But that's why they need their fighter escorts...
Speaking of Ion Weapons, they are another thing that doesn't really make sense mechanically to me. The fluff always talks about Ion weapons creating all this trouble with systems, shorting out shields, etc. but that type of damage is represented by critical hits. Ion weapons have basically the same base damage and WORSE critical hit ratings than laser cannons. Sure, they do target SS but that doesn't really do anything until SS = 0. Also Ion weapons seem pretty rare on stock ships. So I'm not sure they are very effective. Even though SS is much lower for most bigger ships, SS can be repaired every turn. Plus, on your average Sil 4 ship that is armed heavily, you tend to have 1 Ion turrent and 3-4 other types of HT targeting weapons. So you can't even "focus fire" on SS with 3-4 weapons.
Given the rarity of Ion weapons and their fluff, shouldn't Ion weapons have a crit rating of 1 or 2 to represent their system damage capabilities (and maybe laser cannons go up to 4)? That would at least differentiate them more from Laser weapons. They basically become the crit weapons. With a crit rating of 1 you might even get crits with +20-30 added to the roll on a more regular basis. This makes them more effective against bigger ships as well, which is also part of the Ion weapon reputation.