I have actually tried the plier-squeeze method on an old upright piano, and was surprised at the difference it made, and how well the piano sounded afterward. But I'm still a little scared to try the plier-squeeze on my better pianos, but may get the courage to try it at some point. You don't hear much about the plier-squeeze method, but if the hammers are really hard, it could be a good method to use.
That seems like a crude form of the sugar-coating technique, at least as I understand the latter.
At my last tuning, the tech wanted to address all 4 of the hammers needing voicing by filing the hammers. Two of them were well addressed in this way. One of the others has a note that tends toward a more percussive attack than its neighbors. It needs voicing about every other tuning to keep that in check. The sugar-coating technique has been effective in that regard in the past, and I'm thinking I may purchase a sugar-coating tool, and do it myself. Diluted fabric softener might be a permanent solution, but I'm leery of trying it as it is hard to start minimally and increase while testing the effect.
The 4th hammer just needs voicing down. I ask the tech if voicing needles would be needed, questioning whether a filing would achieve the objective, and he said that in his experience filing is all that is ever needed for any voicing issue. That's not what other techs have indicated to me, and the hammer still needs to be voiced down after the servicing.
It seems like what I am asking for is pretty basic and should be in the repertoire of any RPT. Certainly, they are charging at a level consistent with a full service, and not at a level of just a basic tuning.