Nothing disappointing in Episode 4.
Daenerys wasn't expecting Euron to show up and set an ambush for her forces. Daenerys's supposed advisors/allies are at fault - they were too distracted to notice Euron and rather entertaining notions of betraying her behind her back. Tyrion is absolutely conflicted and Varys is not loyal to any King or Queen.
Euron have a presence of mind on the other hand, very sharp and focused.
This TV show is FANTASY, not reality, and it was never realistic to begin with. John Snow should be dead for starters. GRRM can get away with ridiculous positions but not D&D?
Season 7 was fan-servicing work to large extent, and got ridiculed for it. D&D were like f*** this shit, and they took ample pointers from GRRM for season 8 - decent surprises and shock factor in this season.