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 are playing crappy and they have only 8 points more than Chelsea that currently holds a fifth position in Premier League. With 11 matches left for each club till the season ending, 8 points are not too big enough for Arsenal to be sure that they will be in top four. 2 defeats and 1 draw or 3 defeats will be possibly enough for Arsenal to be out of top four if Chelsea play well enough in last 11 matches.
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.