"Maybe" is my (not very helpful) answer, sorry!
Is that a pinned blade you're showing there, I can't quite see? In my experience of pinned blades & machines, the pins "rest" into a little U shaped channel pressed into the blade holders top and bottom. In other words there's no real restraint in the vertical direction, apart from the tension on the blade. So you can try more tension, though it depends on the machine (and the blade) how far you can go with that.
In comparison, pin less blades are most often thinner (front to back and side to side) than pinned blades, so they MAY not twist as much - again subject to tension you apply.
I've found all this a bit of a black art I'm afraid, but once you get settled on a particular blade (type and number) you'll slowly but surely get to the point where you'll "know" how much tension to apply.
Depends on work piece material type and thickness too of course!!!!
Sorry, can't help more.
AES
Edit in the light of your 2nd post: Re a light, please search for a recent post by Claymore and his Excali/Axi 30 "aircraft carrier" where he mentions a little LED light with a magnetic base - called an industrial sewing machine light. There's an e-bay link there. I've now got one now and it's excellent.
HTH
And a 2nd edit (just waking up now). Many/most/all (?) blades tend to cut a bit "cack-handed" off to the right anyway. One of the skills to learn with straight lines is that usually speaking, a straight line cut will not be parallel to the fore & aft blade axis, but will need for the "top" of the work to be a bit offset to the L to get a straight line. I guess this tendency will be magnified with a blade that's already been used for a lot of angled cuts, whatever the tension and type of blade.
"Fun" ain't it?