Would a 100-400 lens be a pointless purchase?

Hi all, this is probably just a case of Gear Acquisiton Syndrome (GAS) or a really middle class problem, but it's my birthday soon and I haven't bought any camera gear for a while so I'm considering buying a new (second hand) lens - specifcally an EF 100-400 mk2

I mainly shoot sport, particularly football (soccer) for my local semi-pro side and my local pro club. For games at both clubs, I use two bodies, an R6 and an R7 with a 70-200 2.8 and a 300 2.8 respectively - lenses this fast are essential for any games in low light, where I regularly find myself at 8000-10000 ISO in order to maintain at least 1/800 shutter speed, so there's no way I'll ditch either any time soon.

That said, I'm thinking of adding the 100-400 to my kit for situations where I'm shooting in decent light, during the day and don't want to take all my kit pitchside with me - I get asked to shoot junior games sometimes, often in the morning before first team matches, and I'm reluctant to take all my gear with me, especially in less secure environments. In these situations, I can see why one body with a 100-400 could work well, and would give me more flexibility to move around and get different shots.

In short, is this a logical or common approach and one that makes sense? Or would I potentially be adding a lens that might only get very occasional use and therefore have little value at roughly £1,300?

Alternatively, I've thought about replacing my EF 24-105 mk1 with a 24-70 2.8, but at £1,000 I'm not sure this is any more worthwhile. Thanks in advance!