Attaching running backstays to mast?

[Brion Toss]

Hello,
First, the load is not entirely in shear. Far from it, it might be primarily in tension, depending on the angle of the runner and padeye. And even if you land the padeye well forward, there will be significant tension on the forward bolts, as well as needless torque on the mast.
I'd either use conventional tangs, independent of the ones for the intermediates, or "lollipop" fittings, which are better than T-balls. Either option would be better for shear and tension loads than padeyes, as well as lighter.
As for the "large hole in the mast," the backing plate for the tang more than compensates for any lost metal. In addition, the tang would be in a region of the mast that is not sensitive to removal of metal, as your rigger should know.
If you go with a T or lollipop, get a fitting that ends in an eye, and splice high-modulus line to it, rather than the usual swaged-on wire.
Fair leads,
Brion Toss