ME3 was more ruthless because the stakes were higher compared to the other games.
The actual dialogue was generally better written than the other games. Shepard's tone during ME3's two big choices come across as forceful yet regretful that such means were necessary. She can also express regret over what happened with Mordin and Wrex as well as reasonably explaining her motivation to the latter when confronted. ME3 also focused the Renegade dialogue thematically on sacrifice.
I think ME1 has benefited from a bit of nostalgia goggles and the fact that fan favorites weren't on the receiving end because a lot of the dialogue especially the Renegade stuff wasn't good. A lot of it was just being rude, belittling people, and obnoxious HUMANITY chest thumping with some really awful highlights like screaming "STAY DEAD" during the Rachni genocide choice. It felt like someone forgot this wasn't Kotor and juvenile Dark Side idiocy shouldn't be here.
While I think ME3 came closest to what they were trying to do with Renegade, it would still probably be for the best if the morality system was dropped. It was already mostly vestigial in ME3 and it feels like the genre has really moved past these binary morality scales.