This isn’t accurate. 20-30% larger diameter with a constant density would mean about 20-30% greater escape velocity (mass is radius cubed but gravity is inverse radius squared, etc). So instead of 11km/s escape, it’d be 13-14km/s. And instead of ~9km/s to reach LEO, it’d be about 11km/s. This is not at all a showstopper. Even in the 60s and 70s, we built rockets with enough stages to go land on the moon and return to Earth, which is a round-trip delta-v of like 14-15km/s, and the Soviets did this mostly with low Isp hypergolic propellants, not even hydrolox let alone an exotic propellant like nuclear thermal hydrogen or electric thrusters. We often just launch stuff directly to GTO or GSO instead of bothering with electric propulsion, so even today’s rockets (many of which also have high enough thrust to weight ratio, like an Atlas V 551) you could do it (and then probably rely more heavily on electric thrusters). Even with higher gravity losses.

It’d be more expensive, sure, but the idea that it’d be almost impossible is just not true at all. It’s a very common thing that even a lot of fairly smart people often say, though.

It certainly wouldn’t be easy, but a massive rocket could get up high enough in a suborbital trajectory where it would meet up with a skyhook or some other vehicle specifically designed to fully boost a capsule the rest of the way into orbit.

That all depends on already having infrastructure in orbit though. I assume the difficulty of such a thing would pale in comparison to the challenge of arriving at that planet in the first place.

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