You can't say whether it's a joke or not subjectively, it depends on which team and how they approach the combine you're talking about. If a team drafts purely on combine results then yes, it's a joke and a waste of time. If a team uses the combine results as a factor and drafts based on it, how well they play in certain situations, what kind of character they are in terms of team work and leadership and they take everything into account, then no the combine is not a joke.
I kind of have the same thoughts as Vincent in the other thread. It's like an exhibition of sorts. No pads, no opposition. It's just pure athleticism. Maybe it acts as some sort of gauge, like what players can ideally do. I'm not a scout so I don't know exactly how they take everything into account.
I wouldn't call it a joke, but I do think teams take too much information from the combine. A lot of workout wonders skyrocket the charts after a great combine and usually bust while a few that don't post great athletic ability often slide. I can think of a pair of MLB (DeMeco Ryans and James Laurinitis) who slide into the 2nd round after less then spectacular combine showings while the list of workout-wonder busts is to big to list. Although Chris Johnson moved up to Round 1 after a great 40 run and the Titans aren't cringing at that pick.
I think the combine can provide scouts with some valuable information on a player, but at the end of the day, lots of teams end up valuing combine performance over game tape, which is kind of ridiculous.