My reason for using SA is not about control, its about reducing the time to arrive at a station by a significant amount.
Select station, engage supercruise assist but fiy at full speed (enable option for manual throttle in supercruise). When 8 seconds left set throttle to 75% to enage supercruise. When 8 ls away max throttle for a couple of seconds then back to 75%. You approach the station at breakneck speed but SA pulls you out onto the station. up to 30 seconds of fairly boring approach flying skipped. Since I learned how to to this I've put SA on a number of ships and always arrive at stations this way.
Also as others have said unlocking guardian FSD booster is not that hard , its one of the first things I did on my alt account after unlocking the pre-engineered G5 FSD. - and once guardian FSD unlocked you can buy as many of them as you like, you don't need to grind the mats for every one.
I see your argument but I still wont put it on my ships, the same with docking computer. For me it feels like it takes up space that I can use for something else, and I do feel like I can arrive fairly quick still to a station in space from supercruise. I think it is personal preference. Also, in terms of interdictions, then I wouldnt know how it will behave. What I think I would need the most help with is to planet land, as I often then not overshooting the target on planets. Which I just read that SCA wont help with. So in all, I still feel like I could use that space it will take for something else, and then steer the ship myself. Even if it means in theory that I will be slower then a SCA.
And about FSD booster, I had unlocked it a few days ago as I wrote to someone else on here. I dont have plans on putting it on other ships currently, but still a part I need for an other build that Im trying to do as to be able to help with the war effort