With the placement of the Control key on most keyboards, your pinkie is doing a straight downwards motion which is much less straining than going sideways, even if it is a bit of a long stretch. Most keyboards (maybe not on laptops though) also have two Control keys so the load is distributed over two pinkies instead of one and neither hand makes any crazy stretches. Personally, I think Caps Lock as Control is categorically terrible advice. I'm sure your intentions were good, but I wouldn't be surprised if this classic trick wasn't originally some vile Vim scheme designed to undermine Emacs users.

Ideal would be to use a keyboard and OS (MacBooks have both) where you can map Control to the keys immediately next to the spacebar. Using the strongest finger (thumb) instead of the weakest finger and the strongest movement (thumb curl) rather than the weakest is a true upgrade.