I think temporarily removing Arsenal from list of club who has secured UCL spot makes sense. 6 points gap to the Forest and 7 to the City aren't big enough if they still play crap.
We're still far away from the end of season. Their fixtures are just getting harder at the end of season. I also remind you they have no strikers at this moment, which is impacting their sharpness.
Various variables are telling us about how Arsenal still in the disadvantages at this moment.
Arsenal’s performance is not so bad that they will not make top 4 if you compare it with other teams as you mentioned. Manchester City, Chelsea and Nottingham forest are not as consistent as Arsenal I don’t think any of them is capable of taking the second position from Arsenal. In my opinion 7 points is enough to keep that spot. Nottingham Forest spot is not secure as Chelsea or Manchester City might be a problem for them but as for Arsenal I think they have secured a spot because they perform better than them all even though they are also having shaky performances.
Their second position can be taken over by Manchester City because this opponent is very experienced and strongly when a season comes to ending weeks. They repeated it impressively with Pep Guardiola in many seasons and dominated the league with titles, so even this season is unexpectedly worse than their normal performance, I believe that they are really able to win against Arsenal for a second position.
I disagree with you here, I don’t think you know how badly Manchester City are playing currently if not you won’t be saying something like this. Manchester city this season are not the team we used to know and we all see how they have been losing and it is not as if they now perform better. They need luck to make top 4 this season.