First, Barbarian doesn't get any damage features worth mentioning after level 5.
I'm very surprised you aren't Paladin 6; cha to all saves in a 10' aura is crazy good. With Hexadin, you can even attack with Charisma, so it can be your high stat.
After you have Warlock 3/Paladin 6, you can have fun with extra stuff. Usually you'd want to go for spell slots, however, to fuel your smites better, or a more reliable source of advantage.
If you are an elf or half elf, then getting advantage plus a 19-20 crit range is very fun with that build; 27% crit rate per swing means you can deliver almost all of your smites on crits.
Rogue 3 is adding a bit of mobility to the build, but not much damage I suspect. I'd have gone AT for the +1 spell casting level (well, I'd first go Paladin 6 for cha-to-saves).
But those are just tweaks.
Yeah, generally agreed. Hexblade 3/Paladin 8 would likely have been a more potent combo overall with minimal to zero loss of flexibility. I'm not really sure those Rogue levels are doing very much other than sneaky skills...which there are much less expensive methods to acquire (like...spending the feat you get at Paladin 4.) If you've a generous DM who lets you take a feat at first level, you could even do Con 16/Cha 15 and grab Elven Accuracy. The vast majority of Rogue skill benefits are front-loaded or massively back-loaded. Expertise in two skills (or one skill + Thieves' Tools) is actually quite a bit for a single-level dip, but 2nd level is literally just Cunning Action which is not worth a level in and of itself, and 3rd is subclass and Steady Aim.
I derped and forgot that they specified Swashbuckler. Fancy Footwork isn't
bad per se, but isn't particularly
great either; the real draw is the +Cha to Initiative, which makes the character very nearly SAD: Hexblade gives +Cha to attack, Swashbuckler gives +Cha to Initiative, and Paladin 6 (when it happens) will give +Cha to saves. Long as you have the Strength to wear heavy armor and acceptable Constitution for HP, this character will only care about Charisma going forward--which is still a bit of a bitter pill to swallow given the
one ASI they've gotten thus far, but it's not the worst thing. Getting Warlock 4 (since Rogue 4 gives nothing but an ASI, while Warlock 4 gives that and a cantrip and another spell known) would finally bump that Cha up to 20...and you'd only be a level 13 character!
It's not the worst combo in the world. Rogue 1 is a great dip, Warlock 3 is a great dip, Paladin is a great class for multiclassing with Cha-based casters. Swashbuckler partially compensates for the otherwise-disappointing benefits of Rogue 2 and 3. I still think the poster above is in a situation where other factors are the major contributor (frankly, it sounds like their DM is, likely unintentionally, throwing softballs and shocked by the results; this isn't hard in 5e, because the line between "not actually giving the players a challenge" and "overwhelming the players" is all too often treacherously thin.)
You probably missed the part where he said "all-around" and where he says he can't outdamage a barbarian.
And then went on to list how they're a better tank than anyone else in the party, doing excellent healing on par with or better than a dedicated healer,
and dishing out Big Dong Damage novas sufficient to make the DM's eyes pop.
Power is very clearly one of the goals here.