I think you are removing too many needles. Needles produce the food for the tree. Removing that many is starving the tree.
Yes, I know foliage are solar panels... and trust me, I would rather not do this tedious work, lol.
But, from my research, this is necessary for bigger niwaki in the wintertime... balances energy for the upcoming year (since apically dominant.. without pulling needles, it would have way too strong of a top and weak lower tree), more sun and air to hit branch's interior for new buds, less pests/fungus, etc., less leggy growth (shade = leggy extension), 2nd and 3rd year needles sag and brown, more sun to lower branches, etc., etc.
Fall should have accumulated enough food for Spring, that's why this is done around wintertime.
I’ve studied niwaki (not bonsai) obsessively for the past 3 years… mostly had to translate because it isn’t done/taught in the US much and these techniques are not done by bonsai people I've noticed (it's only done to niwaki in Japan, and also the rare Japanese gardeners in the US nowadays).
I’ve seen many garden/niwaki pines all over Japan after this ("Momiage") was freshly done, and it looks quite beautiful with the almost bare branches and very visible branch structure…ready for the next season’s flush of fresh foliage.
I've been to 6 cities in Japan and many traditional gardens... and they all do this around late fall and winter.
It is a technique very commonly done in Japan in wintertime for Niwaki (but, not for bonsai I guess, because bonsai are much smaller and need more foliage/energy for health).
I could be wrong though... I'm no expert lol (just lots of research). I just do this from what I've read, researched and have seen in Japan.
This time around, I left 6 pairs of needles per shoot/branch tip end (a good middle ground, not too much nor too little). Kyoto style leaves more, around 8-12 pairs. Also, a niwaki nursery owner here in SoCal told me he leaves only 3 pairs, wow (I’ve seen some of his trees after a fresh pruning too, to confirm... he's been doing niwaki for decades). Last year Dec 2018, I left 3 pairs per shoot (as per that niwaki nursery owner’s recommendation... but felt I needed to leave more this time - 6 pairs).