I can't say that head training Zin is better than spurs or cane pruning, I have seen all training styles used. You do have a lot of blind wood on your cordons, but those cordons look young. Why aren't they pushing shoots? You could train a lateral shoot off one of your canes near the head this year and replace your cordons. Just an idea.
Yup, you're spot on, I'm actually doing that one several other vines where I've had the luck to get some lateral shoots around (or close enough to) the head / upper trunk. Unfortunately this and some of the other zin vines in this row haven't been very vigorous so I have to wait for the opportunity to arise. All the vines in this row are 8 years old, but I made a lot of mistakes early on and only really figured things out in 2021, so I have some technical debt I'm working towards phasing out year after year. In the same row, I had a bunch of missing spurs on this vine and so I used a lateral to start a replacement on the left this year along with a basal shoot out of the trunk (this vine is own-rooted) to fully replace the cordon on the right. I was timid though, and left the old cordons where there was still good spurs in place temporarily to ensure that if these new laterals weren't fruitful I'd still have my old spurs for this season. For the record though, every bug on the new laterals I ran are fruitful, so saving the old buds / cordon wasn't necessary).
The back-story here, is that 2020 was my first yield, but I both over-cropped that season (no cluster thinning) and under watered while we had 3 consecutive days of 112 to 115 degree heat over labor day weekend (I've since learned to watch the weather / leaves / tendrils and water extra when it's really hot). It fried my zin vines the worst, actually boiled a bunch of the grapes, turning them from dark purple to brown in a matter of days. After that, I lost a lot of cordon and spur positions, which I only realized in the spring of 2021 when pruning and finding all the dead wood. So it's been a long haul of working my way back to healthy vines.
I do agree, the vines look young, compared to my merlot, cab and tables grapes the trunks and cordons are a fraction of the zine. The best I can do is chalk that up tot he fact that they've never had much vigor due to the shock my mistakes in 2020 caused them. That's just my best guess, but that's why I'm here, to learn and maybe find some answers to these types of questions.