Meanings change with usage often for the worst but also for the better.
Etymology is fun but also a form of necrophilia if it's used to cling to a the rotting corpse of a word.
Grandfather has it's own problems:
a) grand (adj.)

late 14c., grant "large, big" (early 12c. in surnames), from Anglo-French graunt and directly from Old French grant, grand (10c., Modern French grand) "large, tall; grown-up; great, powerful, important; strict, severe; extensive; numerous," from Latin grandis "big, great; full, abundant," also "full-grown;" figuratively "strong, powerful, weighty, severe," of unknown origin.

In Vulgar Latin it supplanted magnus and continued in the Romanic languages. The connotations of "noble, sublime, lofty, dignified," etc., were in Latin. In English it developed a special sense of "imposing." Meaning "principal, chief, most important" (especially in titles) is from 1560s; that of "of very high or noble quality" is from 1712. As a general term of admiration, "magnificent, splendid," from 1816. Related: Grander; grandest.

Grand jury is late 15c. Grand piano from 1797. The grand tour of the principal sites of continental Europe, as part of a gentleman's education, is attested by that name from 1660s. The Grand Canyon of the Colorado River in western U.S. was so called by 1869, popularized by Maj. John Wesley Powell, scientific adventurer, who explored it; earlier it had been known as Big Canyon. For grand slam see slam (n.2).
Bringing PC into the discussion is conflation.
&
b) grandfather (n.)

early 15c., from grand- + father (n.), probably on analogy of French grand-père. Replaced grandsire and Old English ealdefæder. Grandfather clause originally (1899) referred to exemptions from post-Reconstruction voting restrictions (literacy, property tax) in the U.S. South for men whose forebears had had the right to vote before 1867 (thus allowing poor and illiterate whites to continue to vote). Grandfather clock is from 1894, originally grandfather's clock (1876), "a furniture dealer's name" [OED] from "My Grandfather's Clock," the 1876 song by Henry Clay Work that was enormously popular (and loathed) in late 1870s. It indicates that they were beginning to seem old-fashioned; they were previously known as tall case clocks or eight-day clocks.

Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe