KWP. He was at his absolute best for us when he was given the freedom to make those marauding runs down the wing and cause havoc in opposition defences. But we don't see anywhere near enough of that from him these days because of Russ's 'play it safe' mentality. He's being shackled and doesn't look happy.
Tall Paul. Proven goal-scorer throughout his career. Clearly gives opposition defenders nightmares in the few cameo appearances we've seen from him so far, but we don't play to his strengths because our slow, ponderous build-up play gives opposing teams too much time to organise themselves defensively and mark him effectively. In all his minutes so far this season, I think I can count on one hand the amount of times we've actually tried to cross the ball to him.
BBD. Again, proven goal scorer in the Championship and has shown he is also capable of getting goals in the PL when employed as a traditional, physical centre forward. So what does Russ do? Sticks him out on the left wing where he looks completely lost because he has none of the attributes needed to be an effective winger.
Fraser. I don't know what's going on with him/his form this season, but he has performed at a higher level in the PL in the past so clearly doesn't fit with your description of "basically doing as well as they have at any point in their career". Again, if he were given the chance to play and licence to actually run at defenders in the way that we know he can, he would cause problems and create openings. But Russ seems to prefer Manning in that position these days.
ABK. OK so something weird has gone on behind the scenes, and I guess we'll never know the full truth of it, but the simple fact is we have a German international CB who has looked decent for us in the past (he was excellent for us before his shoulder injury), who says he is fit and ready to play but is being left out of the matchday squad completely. Maybe with Bednarek's injury he might get the chance to prove himself again, but I'm not holding my breath.
Big Les. Clearly has talent and physical strength, but has really struggled in his recent appearances because he's being asked to play in a position that doesn't suit his strengths. Whether or not he will go on to be a successful PL player is still in doubt, but we'll never know until we play him in a position where we can get the best out of him. The famous Einstein quote about judging a fish by its ability to climb a tree springs to mind.
And finally an honorary mention to the now departed Charly Alcaraz - who was genuinely the most exciting player I've seen in a Saints shirt in many years but was allowed to leave on the cheap because he was too unpredictable and wasn't suited to Russball due to taking too many risks in the final third.