I agree with you; the biggest surprises of the tournament so far have been in Group E. If Belgium suffers another defeat, they may not be eliminated because they can still qualify out of the group as the third-placed team. However, this situation would make their job harder. Considering today’s performances, it is possible that Ukraine will finish last in the group, and Belgium will end up third.
This is just their first game and I think it is way too early to judge them base on this performance today alone, The game is still open and Belgium can still come out top in their group if they win all their remaining matches from here despite that they lost in today's game but the correction may come in their games ahead, and I still doubt Belgium won't qualify for next stage of this competition.
Yes I agree with you that Belgium can still come behind to top the group as this is just the first leg of the group stage level, but there is one thing I have observed so far for all the games that have been played so far, those big football Nations that are always good in every tournament, are literally struggling to maintain a win or score more goals, take England vs Serbia for instance, that is a game we would have thought England could have scored more goals but the game ended 1-0 in favour of England, France where only able to win Austria with just 1 goal, these are countries i would have expected more goals from France considering the calibers of players they have. anyways it was good to see n'golo kanté win man of the match for the France game against Austria.