Yeah iirc Death Star II once completed would've been impervious with no outward weaknesses. The path into the main core I assume would've been sealed up once construction was completed.

Hence why the Emperor allowed the Rebels to find out the location of Death Star II, knowing it was too tempting a target (or the only chance to take it down) whilst under construction.

The Battle of Yavin makes more sense from an in universe point of view now because the Rebel fleet was smashed about two days before hand, which is why there was no cap ship support. Red and Gold Squadron arguably get wiped out so quickly probably because they're so combat fatigued.
Actually the pre-battle Yavin briefing in ANH makes it clear that capital ships would be decimated by the Death Star's main defenses consisting of turbolasers (can't be bothered digging up the quote). I'm sure the Rebels had other fleets in reserve but starfighters were clearly the way to go.