Brown, for sure, was (is?) the bigger figure. But let's look at the similarities. Both chancellor, both took difficult financial decisions during a crisis (global financial crash / COVID), both went on the become unelected prime ministers, both resided over imploding parties, both utterly devoid of charm port warmth as PM (remember Brown chairgate?), both doomed to fight and unwinnable General Election. I don't think Sunak use trying to make himself look like Brown, but he is in many respects.
I never actually used to like Brown growing up. It genuinely was the charmless sulk vibes he had. But on reflection he did a lot of difficult work when in office and put in place sensible policies that lead to growth. I just think he was never destined for the top job and he should never have taken it. Some people are just better at being back office workers, and I don't mean that as a slur. I'm actually now really impressed with what he's done out of office, his ideas for how to hold the Union together and bring prosperity to all party's of the UK are really worth thinking about - something I hope Starmer takes on board
Sunak is.... well. A caretaker for a year.