I won't get in the way of ahill and Future Warrior's debate, at least not for now, though I'll offer my thoughts on the matter.
For the most part, I'd side with Keedounan and ahill. There is some level in which I can agree with the opposite viewpoint in that it's only after Freeza's death (both assumed and actual) that Vegeta is given the full opportunity to live as his own individual and live how he wants, with traits that came from his royal lineage and some influence of Freeza's personality manifesting themselves within his actions. Still, that doesn't justify his complete change in approach to battle as Keedounan went into or how deluded he became by Super Saiyan's hype when, by all accounts, he should know it to be far from invincible. Not just that, but his attitude to Goku spits in the face of his death scene on Namek. 'Member when Vegeta used his dying breaths to declare Goku a Super Saiyan and entrust the pride of the Saiyan race with him? Apparently Vegeta didn't.
sei'taer said:
And Namek arc vegeta didn't believe he was turning into an invincible Super Saiyan the whole latter half of the arc?
Back then, he didn't have a solid grasp on what a Super Saiyan actually was and was going entirely on what was told in legendary accounts. In the Cell Arc, it's made apparent to him of the physical and Ki traits of one as well as proof by one that they weren't some invincible warrior.
That let Freeza transform because he was positive that he wouldn't get that much stronger?
That was far from the only reason Vegeta let Freeza transform. With Zarbon as his only benchmark for what to expect, there's no reason Vegeta would assume Freeza couldn't transform instantly. That said, what use would there be in having himself, Gohan and Kuririn wear themselves out fighting 1st form Freeza only for him to transform instantly and make their slim chance of winning even slimmer?
The Freeza case is far different than with Cell, in which he had a complete grasp of Cell's current limitations and still did nothing to prevent Cell getting stronger.
That got super enraged the entire fight in the arc previously that a simple low class saiyan like goku had surpassed him?
Back when the idea of a low-class Saiyan or any other Saiyan, or anyone outside of Freeza's elite troops for that matter, coming close to or surpassing his level was something he'd never before witnessed or imagined. Compare this to in the Cell Arc, where that 18k figure is a joke when it comes to power, he's met many fighters capable of rivalling or surpassing him and, as I mentioned prior, respected Goku's power enough to entrust the vengeance of the Saiyan race and their pride with him.
The two situations are only comparable when removing context to get rid of what development and growth the events on Namek gave Vegeta.
Kyo said:
Always had more of an issue with Boo arc Vegeta personally.
I'd agree somewhat to that. I'd say he dropped the ball harder when it came to the reason he had for going Majin being more petty than letting Cell gain his Perfect form, though I'd say the wiggle room he had to work with in terms of estimations for what to expect from Perfect Cell's imminence as opposed to the possibility of Boo's revival were far more of a risk. As he later alluded to with his talk about Kaioshin not living up to the hype and how strong he and Goku had become as well as his mention of Dabura not being some major threat prior despite his status, there was still a fair possibility of Boo not measuring up to what was at that point the peak of power. Meanwhile, 2nd form Cell was still capable of making Vegeta's lip bleed, so estimating he'd be able to take Perfect Cell with how little he had to go on in what to expect was way more of a gamble.
Also, whilst it could've used more time, the catharsis to Vegeta's character arc was at least far less rushed than what the end of the Cell Arc did for him.