Adding my two cents in this discussion. I'm truly glad there's more of us who dislike the ending scene at the docks. It made me feel so awful the first time that I cannot finish any more playthroughs...well, unless I choose to ascend him which...yeah, I just cannot stand the ascendant, but seems like Larian is pushing me towards that route solely for the fact that I won't have to watch him run away while my Tav stands there with zero reaction + the companion comments make it even worse. This is supposed to be the good ending? That makes people feel miserable? Because I sure did feel like that.
I get it, the tadpole no longer protects him but that doesn't mean it had to be portrayed this way. He's the only one who loses when the worm is gone, why isn't it treated with more respect? Especially since all the companions were so proud of him before.
It would be great to expand upon his quest after defeating Cazador - finding some item that'd protect him from the sun (maybe for definitive edition). For now it'd be enough to re-work the ending scene. Apparently there was supposed to be a whole bit at the tavern but it was removed/not implemented. That could've been a proper sendoff, saying goodbye to everyone properly before they go their own way and then we could talk to our romanced partner. Instead we get this abrupt cut which is especially jarring when it comes to Astarion. How did he get into that room, was he waiting for sundown or where exactly is he? Tav cannot even ask him "are you alright?"
Moreover, it doesn't feel like it's two people in a relationship talking and the conversation is way too short. There should be some hug + kiss included in it, instead of standing so far away acting like acquaintances (apply to all companions of course, not just Astarion).
Lastly, spawn ending has less 'screentime' and dialogue (at least how I see it). With ascendant there's the whole turning into a spawn scene, the conversation afterwards, and a lot of questions you can ask him later, etc. For spawn, once he's done mentioning Cazador and thanking Tav, it's over. The only option we can pick is the lame "you don't need the powers of ascendant, I'll protect you" ...which I found kinda tone-deaf. He's not some damsel in distress in need of Tav's babysitting. Especially since before he talked about him and Tav being equals. So I'd like this option replaced with something like "we will protect one another just like we've been doing it till now" and I'd love some other things we could do - let's say burn down Cazador's mansion and make a bonfire out of all the tasteless art and watch the carnage holding Astarion's hand. It would be a lot of work to implement but would help for his story to feel less dead in the spawn ending IMO.