Well spotting yourself with a pole is mostly about familiarizing yourself with the movement. It doesn’t really matter how much you use your arms in this one, because the rebalancing is what’s diminishing the difficulty of the movement, not the actual strength of pulling from your upper body. Try spotting yourself with just one finger, and you will likely find that it still makes it much easier, even if you don’t feel like your finger is pulling very hard.
To work the strength for pistols you would do the wall sits or elevated pistols. I prefer wall sits though because they’re different enough from full pistols that they are more worthwhile later on when you do get the pistols.