Group E surprised us, Romania managed to finish in first place beating Belgium which on paper could be much better. Maybe facing the Netherlands is not easy, it's just that in terms of opportunities, Romania still has the strength to put up a fierce fight, the round of 16 is definitely a strong reason for Romania to play at full strength.
Slovakia is not a top team that can progress further, England should be able to handle this well but even that is not 100% if you look at England game which always has difficulty finding the ideal formation. Southgate is considered a rubbish coach who is unable to utilize his star squad.
Compared to Belgium, which will face France in the round of 16, I think Romania is a little lucky against the Netherlands in the round of 16, even though it is equally difficult, Romania still has the percentage to be able to beat the Netherlands in the round of 16.
In the Group E phase it was quite fierce and I think Romania's success in becoming the leader of the standings was because Belgium did not perform well at this Euro.
In the group phase, England have not shown an impressive performance, but I don't think they will have any difficulties in the round of 16 against Slovakia.
And what happened in the group phase cannot be used as a reference, there is still a big possibility for England to improve their performance if you look at the squad they have.