It's more reliable than, say, down smash (obviously) and many more. I'd say its a main KO move, along with the other ones you listed. Those you have listed are almost never used on the ground, so in ground combat f-smash would be a great KO'er. Its not useless. The tipper is very good and more useful than you give it credit for.and Fsmash isnt a main killing move at all. It does incredible damage and knockback when its tippered (24% uncharged, more knockback than luigis fsmash) but if its not tippered its extremely weak, probably wont even kill until 130. Its long start up time just doesnt make it a useful KO move at all. Backthrow is #1, then maybe bair and uair close together. Id rate PKT2 more of a useful KO move than his fsmash
Though, I agree that the startup lag is annoying for not having much range to work with. And, as I said before, vs. Lucario, f-smash's range gets domitated by ours.
EDIT: Anyone disagree with my analysis of the matchup? (see post #991)