It's possible to be both these things Del. Both a "squad player" and someone who helps turn a game. We only have to look at Origi to see that. And Shaqiri had his moments too.
The frustration with Keita (I feel it anyway) is that he's a far superior player to both these two, yet the dividend is about the same. And although we are not meant to mention his transfer fee ("not his fault", "not our money" etc) it must have reflected a belief in Jurgen Klopp that Keita would be a central pillar of our team. It hasn't quite happened though, has it? Maybe it still will. But it's been a long wait.
Then why isn't he an automatic starter when everyone is fit?
There are reasona for this, though. I've written about them at length in this thread (and more in depth elsewhere) and I won't bore people agian with chapter and verse. But the short answer is that the tenor of our midfield and the nature of our creativity changed between our deciding to buy him and taking delivery of him, and between his arrival and his being fully available (remember he got injured in his first season shortly after arriving).
There was no flick of a switch, as such; but things evolved fairly rapidly. Before we got him we were still at the tail end of our midfield being a standard holding/creative force and fullbacks still traditional in role. By the time he arrved this had started changing, and by the time he was fully fit again after his first injury lay-off, the change to a functional midfield and our trademark full-back-supplied creativity was complete.
Suddenly the very specific reasons he was perhaps bought for had become...not redundent, but less pivotal. He now had to secure a role for himself in a more functional, power-based midfield, harrying and pressing, fire-fighting and covering for the fullbacks, rather than his more vertical game. Fabinho arrived and Wijnaldum became a mainstay for reasons that were very different to Keita's game. It's not surprising that he failed to oust Gini as a starter.
In short Klopp preferred to deploy tactics Keita was not best suited to and to stick with a deployment that worked. This meant that even when fit Keita did not get as many starts as may have orginally been planned. Circumstances had changed.
More than anything he has been a victim of those circumstances. And he wasn't alone. Lallana also suffered in this way.
So it's not a surprise and should not be seen as a bad mark against him that he has not been able to produce his A-game very often. The Leicester game is a perfect example. Many of us wanted him to start and certainly to come on when things weren't going well. He did come on but he was instructed to play in a way not suited to his strengths. It was frustrating watching him NOT doing the things we thought could open them up. But they were his instructions, for whatever reason.
The good news is that we are evolving our midfield game at this precise moment and this season more than others he has shown what he can do at the top of the midfield, pressing, dodging, ball carrying, passing, interlinking and attacking, as well as his defensive work. When all are fit and covid free there's a clear role for him that is more suited to his A-game and that is more akin to what we expected from him before he arrived.
Now's not the time to give up on him