I actually thoroughly disagree with this opinion. The choice Syrskyi made in Bakhmut was controversial because, as you alluded to, the last 6'ish weeks that Ukraine stayed in the fight there, the casualty ratio was closer to 1-to-1 compared to the much better ratio Ukraine enjoyed earlier in the conflict.What they did in Bakhmut was wrong, and a repeat of that would also be wrong. One of the reasons why Syrskyi is not trusted by the Ukrainian military is exactly the bad strategy he had in Bakhmut, because he retreated too late.
In the initial part of the offensive (both Balhmut and Avdiivka), the Russians were losing at a disproportionately high rate compared to Ukrainian defenders (some sources say 7-1 losses). This is when it was a good strategy to defend and bleed the Russians. But once they got into the city in Bakhmut and started to fight house by house, the loss rate evened out to approximately 1-1. This is terrible for Ukraine, because losing 1-1 against Russia is clearly in favor of the Russians who have a much larger population pool.
Once the Russians entered the city, the Ukrainians should have retreated, to avoid the 1-1 attrition rate of the house to house fighting.
Syrskyi made the wrong call In Bakhmut when he overstayed at the expense of many lives, and it seems that the same mistake is being made in Avdiivka now. The Ukrainians should have already left Avdiivka, once it was obvious that the retreat is inevitable and becomes more dangerous by the day.
Ukraine needs to conserve its manpower and inflict maximum damage on the Russians with minimal losses. Any fight that doesn’t have a very high casualty ratio in favor of the Ukrainians is good for Russia.
But Syrksyi didn't leave troops in Bakhmut and actually further reinforce it, to get his troops killed. He did it for two very important reasons that have quickly been forgotten.
1. His primary goal was to make Wagner combat ineffective moving forward, by inflicting extraordinary loss on their manpower and armor. Wagner was Russia's nost effective fighting force at that point in the war and by forcing them through absolute hell, despite his troops facing the same reality, more than 20,000 Wagner fighters were KIA in the Bakhmut offensive and it was their last gasp of the war, before disappearing into irrelevancy. That would have been a horrible decision to have to make for Syrskyi, but ending Wagner's campaign in Bakhmut was a national priority at the time, and the objective was achieved.
2. His secondary goal was to force Russia to divert forces to Bahkmut to reinforce Wagner, to alleviate pressure on lesser defended areas of the front, more vulnerable to Russian breakthrough. Russia diverted an estimated 14,000-17,000 troops to Bakhmut to reinforce the Wagner effort. Those troops had been planned to be used elsewhere. By Syrskyi holding out in Bahkmut as long as he did, Russia was forced to commit those troops to the assault as well and they too went through the meat grinder, meaning that they weren't able to be immediately deployed in effective fashion, after the Bahkmut campaign.
Yes, Syrskyi, in that one instance, chose to sacrifice Ukrainian loves for the greater war effort. The move was heavily criticized and will remain so into the future. But such are the decisions that Generals have to make. A war with a front this large, has many factors to take into consideration and when / how you choose to fight vs retreat is critical. I tend to believe that Syrskyi calculated for how long Ukraine could withstand a 1-to-1 casualty rate and chose that option because he had the "big picture" of what was happening on the ground, in the war, at the time. He chose the virtual elimination of Wagner and the tying up of additional regular Russian forces for months.
Note that Syrskyi was also the commander in charge of the defense of Kyiv and that turned out to be a brilliantly, executed plan, which was not nearly the meat grinder that Bakhmut was. It's not as if he has used the same plan, at every point stop, and not achieved results.