The Transmission and Whale Capture Plan make no sense

Why would Admiral Kirk bother to send the message of 'we will time-travel and save the planet' to Earth at a point where the Earth is almost destroyed?

I mean, they DO plan to come back to a much earlier moment in time, or there'd be no point in trying to save the planet, when it's already destroyed (for all intents and porpoises (sic) anyway), right? I mean, they indeed DO arrive at an EARLIER point in time, which means there are two Klingon vessels with our heroes inside existing near the same spot simultaneously..

My point is, why would Kirk waste time to send this kind of useless message, when they are bound to alter the timeline in order to save the planet (and the solar system), so that the devastation never gets as far as in the unaltered timeline, so because the planet is saved before any and all of this can happen, the message is not only unnecessary, but also erased from existence/history!

Of course, in the same token, you could say that they never go back in time to get the whales, because there is no devastation because the whale-plan worked, so there will be devastation.. well, typical time-travel paradox, really.

In any case, Kirk wasted valuable time in a crisis situation by sending a message to basically dead people, that then never get the message, because Kirk (and the crew) ends up altering the timeline anyway so now they are 'alive people'. Completely useless and brainless thing to do, and thus makes no sense.

The whole 'capture the whales'-plan also makes no sense, because Spock not only can, but DOES indeed 'mind meld' with one of the whales (Grace?).

This renders the plan completely redundant and useless, because the mind-meld affords a MUCH easier alternative! Still don't get it?

Well, they can't just capture whale sounds and bring it into the future, because they don't understand what it means (though the 'songs' themselves are probably as much information as 'smoke signals' or 'jungle drums' of the olden times - the point wasn't to actually send DATA or messages through those methods, but to ALERT the 'shamans' (for the lack of a better word) to initiate a telepathic communication in meditation and such. It's more like a notification that now we can be online than actual message)..

..BUT, because of the mind-meld, Spock could tell the whales of the problem, the whales would know what to do and say, then Spock could tell them to wait for 30 minutes or keep some kind of telepathic contact or whatnot, so they would give the whales signal, so then the crew could capture the whale audio with the Klingon vessel, and once it's complete, they could jump back to the future, play the message to the probe and it would be the same result.

Right? RIGHT?

I mean, why go through ALL that hassle, when all they needed to do is to have Spock tell the whales what to say, then play that back to the probe. No need for transparent aluminium or changing history (the whole 'how do we know he didn't invent the thing' is actually really stupid as well, because they SHOULD know who invented it, so they wouldn't alter history! Even tiny change can mean Sulu will never be born or whatnot).

In any case, this is a great, classic movie, but I am saddened to notice that even my favorite movies have ridiculous nonsensical parts, if not downright plotholes about them.

I wish at least good movies would make sense, even sometimes. Sigh.