The problem is more on Nintendo's end, you can't really get much personality from TP Ganondorf since he doesn't say much. Would you think the same about WW Ganondorf if he hadn't had his monologue? He would just be plain bad guy Ganon trying to get the Triforce, there's no saying whether TP Ganondorf thinks the same or not, since he didn't give the same speech. I think it's safe to assume that his backstory is somewhat similar at least, since even though they are in separate timelines, they are both actually Ganondorf from OoT, under different circumstances. In either case, he was still the Gerudo king, he still tried to take over Hyrule in OoT, and failed in both instances, it's only the events afterwards that changed massively.
It doesn't matter. WW Ganondorf isn't in Brawl and TP Ganondorf is. TP Ganondorf's personality is that of a completely cold and calculating person, as well as serving. It's the same in Brawl. WW Ganondorf does not exist in Smash. It doesn't matter that their younger counterpart is the same person. They
aren't. I don't see anything alike with them whatsoever personality-wise.
So I don't see why Ganondorf in Brawl would ever be a person similar to R.O.B. If it was based upon WW Ganondorf, sure(and if he showed an appropriate personality to him, which he doesn't). They frankly are nothing alike. Ganondorf is still evil incarnate who took revenge for Master Hand in Brawl, pretty much the only reason for him to team up with the Heroes. R.O.B. has a similar situation. The difference is that have entirely different backstories. And even if it was WW Ganondorf, he
still lacks a Brawl backstory. He's just serving what he thinks is Master Hand and we're told nothing more.
If it's just the earlier Ganondorf doing so(as in in Brawl it's the same person growing older), well, he was only presented as a bad guy in Melee regardless, working with Mewtwo(who shared the same fate) and Giga Bowser(a villain). Possibly all working for Master Hand for all we know. I mean, in Event order, you face off against the Hands, then face next an even more powerful foe. But who knows exactly what the ideal story is.
As of Brawl, he's just a bad guy working for Master Hand who was clearly loyal to the hand and wanted to stop Tabuu essentially because of that. The fact even Zelda and Link were willing to work with him is amazing enough. They had a common enemy, which apparently is good enough for him.