I'm a bit puzzled by the notion of losing precious years. An old tree struggling for centuries on the edge of death is the very look I'm going for. The tree is already there - it's not going anywhere. The only way I'm losing anything is if it dies, but I think it will not be difficult to keep him on the living side of that edge if this is only done periodically, with periods of rest in between.
What I meant, by losing years, is that in bonsai, the faster growing and the more vigorous the tree is, the faster we arrive to our design objectives. So, we want to speed up the growth, and not to slow down. Once the final branch structure is in place, along with the desired girth/taper, THEN we can slow down the growth.
In the case of this juniper, you are slowing it down before the structure is there. I am tempted to do the same thing with my junipers, but after many years, I am finding out from more experienced growers that this approach is too simplistic an lacks a deeper understanding of how to develop juniper bonsai in optimal time. By hard pruning a shimpaku, we are taking the longer, slower, and riskier approach. No reason for it, really. The consensus is that you should leave no less than around 60% of the foliage, in order no to interrupt the healthy vigor of the tree. Of course, most of that foliage will be gradually removed as we approach the final design, so for now, they are sacrifice branches.
BTW, when doing the same thing to a red(or black pine), which is hard pruning, the result is quite different: a strong flush of new growth. Same with deciduous trees. Junipers also respond with new growth, but the overall growth rate slows down considerably. This is where our mistake lies: to treat junipers the same way we treat other trees. The pinching vs pruning is not the issue here, nothing wrong with pruning.
The approach changes when the design is "finished", and slowing down the growth becomes appropriate, although I would not like to keep a tree anywhere near that edge that you re talking about, but rather make the impression that the tree is close to that edge. When the tree is truly on the edge (albeit on the right side of it), there is very little room for mistakes, or simply a random negative event.