You're correct - the true type files have 'sc' fonts that look pretty good unless greatly magnified. With FontCreator, with glyphs-magnify options, the individual glyphs are very crude compared to commercial (or even the better class of non-commercial ones), but they should be adequate for epubs. And perhaps the font author intentionally incorporated the crudeness to emulate the old type.
I didn't realize that the otf and the ttf fonts differed - previously, and this time before you pointed out the difference, I had downloaded the otf fonts and found they did not have keyboard useable sc fonts. The true type sc fonts have the proper sizes of 'capitals' and 'lower case' and I think they should look much better than my usual small cap fonts or the Sil tuned small cap fonts.
Thanks for pointing out my incorrect assumption about ttf and otf!