@mage_goo
well, the examples you gave of killing the dragon, the tyrant, and freeing slaves was an example of their lack of follow through. In each case, they see it in terms of a game or story, ones with a limited scope with a neat and tidy end specifically. Further, they aren't really isekai hero stereotypes, they are isekai reader stereotypes. The reflect a person trying to act the part of an isekai hero.
The sword hero will be criticized later for killing the dragon that actually wasn't doing anything but only by the dragon's daughter. As for what Nao and the story up till this point criticisms him for, it was that he didn't finish the job because he either thought and that the corpse would disappear or that he simply didn't know that leaving a giant corpse to rot near the village would be a biohazard. This matches his motif, since he's the youngest and represents younger isekai readers who think Kirito is cool, specifically for being a loner. Half the time, his problems just that he doesn't know better yet and he often responds reasonably to criticism. The other half though...
The bow hero's attempts to act the part of a more typical shounen hero and his vanity is pretty obvious. As for the thing with the tyrant, it's actually a pretty serious real world problem. There's been plenty of wars and revolutions which have been carried out without consideration for who has power after the tyrant is killed and these leave a power vacuum which lets someone worse come in. It would be nice if just killing the head fixed the problem but it almost always makes it worse. So he's just acting out the exciting parts of a story with no understanding of how to deal with the problem itself. The english version of the LN is actually just about to get to the part where Nao will have to do this kind of thing himself and seems to do a better job of it, so we'll see how that goes.
The spear hero's pretty much the manifestation of kronix and those like them. He's trying to act out his idea of a "good" hero when his only real metric is if he sleeps with the harem, the reason for that earlier scene where he was concerned about Bitch robbing the townspeople but shut up when she started to flirt with him or something(they didn't show much of his reaction in the manga). As for his thing about trying to free a slave (Raphtalia) the problems are as Raphtalia and Nao mentioned and then some: he's only concerned because said slave is attractive, he doesn't have the actual ability to free slaves or enforce their emancipation (he has no real political/judicial influence and the nobles will simply do as they please in the shadows as he's really just one guy who can hit stuff hard as long as the nobility or other authorities don't choose to back him), and the biggest problem I believe is what happens after they're freed. In the US, the emancipation of slaves was a half-measure, as the 13th amendment allows slavery under the condition that they have been convicted of a crime while former slave owners can then target specific behaviors, substances, or just being a specific race at a given location in order to re-enslave them. In this story, slave traders will be attempt to re-enslaved someone simply by catching them again. Later, when Nao has more political influence, he'll set up a system for dealing with this somewhat.
TL;DR
the problem with the heroes is that, before they get their own reality checks, they are dumb isekai novel readers trying to imitate the heroes in poorly thought out stories. Even if dealing with a problem itself is good, they either don't know enough about the problem or don't care enough to try and fix it without making it worse.