Grape trellises work best if they are in the form of a “T”. I use 8 ft T-Posts and weld a crossbeam at the top. I drill holes in the cross beam and run two wires separated by at least 3 feet horizontally. Good bracing at the end of the row is required. You can use a 45 degree angle brace or can use posts driven into the ground with wire and a turnbuckle to keep it tight. I don’t like using the wire and turnbuckle because it makes mowing difficult. 45 degree angle braces work fairly well because the brace is under the vines which suppress grass growth.
Why use only two wires? The way I have my trellis set up, I can mow under the vines if I choose. When picking grapes, they are at head height which allows me to walk under the vines. Sunlight collection with this type trellis is maximum.
Some international vineyards use up to 6 horizontal wires to increase sunlight capture. Vertical trellis such as the diagram you posted are rarely used. There are too many limitations in terms of production, difficulty pruning, difficulty picking the fruit, etc.
As you note, it is almost impossible to drill holes in T-posts. I found some extra hard drill bits that can do the job. However, I don’t recommend drilling T-posts because bolted on attachments are subject to problems when fruit load is very high. U-bolts are a better alternative. Put one on the T-post and drill holes in the cross beam to fit. Clamp down the U-bolt and it will be as solid as a welded on attachment.