While I don't think the companion writing in Pathfinder is the greatest, I do think a lot of the problems are design and structural. More so in Wrath than Kingmaker.
The companion content to game-time ratio is definitely a part of the issue. But the bigger issue for me is how that content is delivered. The PF games are pretty formulaic in how they stretch out the companion content across the game. The way almost every companion quest gets a few mini-quests spread across Acts, and are always structured (sometimes unnaturally) to have the player wait in between. This kills the momentum of many of the companion stories and the overall emotional experience. They essentially push the player to be passive about their companions' goals and motivations (i.e. "it's not really urgent, just wait"), and consequentially highlight how secondary those are to everything else that is going on.
For example (WoTR Seelah Spoilers):
Take Seelah's companion quest for example. During the wedding tragedy in Act 3, the game does all this work to set up a problem/scenario, and provides motivation for the player to act (i.e. to track down the culprit and save the victims in need). Instead of the quest progressing naturally towards a urgent rescue mission, it just... ends for Act 3. That's it, the journal tells you to wait, and you completely forget this until Act 5 (potentially 50+ hours later) to resolve this.
Seelah's personal arc is basically put on halt, and by the time this actually resolves in Act 5, I barely remember the culprit or the victims because SO MUCH happens in between. The emotional weight of this quest is now competing with all the main plot revelations and world developments since.
Stretching the companion resolution into the final acts also means they get lost in the cascade of arcs and climaxes that comes from the main story. There are some big moments in Wrath, and I think having a bunch of the companion arcs resolving in parallel to those moments make them feel very inconsequential. Some of the companion stories do fit with the "waiting between Acts" format more naturally than others. But overall I think the format actually detrimental.
Overall, I do find the companions of Kingmaker more impactful than Wrath because they're better integrated structurally into the main plot.
Kingmaker Spoilers:
Despite being a bit railroady - the companions just feel more plot essential in KM versus WoTR. From Tristan's betrayal, to Linzi's death, to the separation and resolution in the House at the End of Time. There are multiple moments in KM where your companions are in the forefront of the story, driving the plot due to their agency. Compare this to Wrath, where there really isn't these kinds of moments where your companion gets the spotlight in the main path. You get a weird non-party companion battle at Threshold, but that is completely inconsequential to the ending.
