I don't know how anyone can possibly argue that Zimbabwe is better than Rhodesia or that Mugabe was better than Ian Smith with a straight face. Setting aside how much worse off Zimbabwe is compared to Rhodesia in basically every measurement of living standards down to the most basic one (food security or lack thereof, as has been memed to death, like many a starving Zimbabwean), almost immediately after winning,
Mugabe embarked on a genocide of the Ndebele & Kalanga peoples who supported the rival ZAPU faction (which had also opposed the Rhodesian gov't but was more ethnically diverse than Mugabe's own ZANU, a primarily Shona-based and increasingly obviously Shona-supremacist group). In just four years Mugabe managed to kill 20-40,000 people, mostly civilians who were just unfortunate enough to have been born to the wrong tribe, while
the entire Bush War saw a maximum of 20,000 casualties (black and white both) over 15 years and
slightly more than half of those were combatants (of said combatants, the ratio was a lopsided 10:1 in favor of the Rhodesian military).
There's literally no reason whatsoever that one should consider the Rhodesians worse than the Zimbabweans who toppled them. Even in racism they were objectively far outdone by Mugabe and his horde of all-destroying thugs, Smith never stooped to actively genociding his enemies despite arguably having a far better reason to do so than Mugabe (the Rhodesian whites, as a minority, would have benefited more from engaging in 'population reduction' of the blacks - regardless of tribe - than the Shona did from genociding the Ndebele, as the Shona already comprised a supermajority of Rhodesia's population). Rhodesia didn't have apartheid (its restrictions on black political life were milder than those of South Africa)
but even if they had it still would've been better than pulling a proto-Rwanda on rival ethnicities as Mugabe and ZANU did.
The worst thing about the whole debacle, I'd say, is that there really was a middle road within reach that would have tamped down on the worst aspects of the old Rhodesian state; significantly expanded black political power; and empowered moderate figures in the black movements while marginalizing the likes of Mugabe. Said moderates, led by Bishop Abel Muzorewa (basically Rhodesia/Zimbabwe's Wish.com Desmond Tutu), had negotiated
the 'Internal Settlement' with Smith's government to turn Rhodesia into
Zimbabwe-Rhodesia and
hold elections with an expanded black franchise that were considered free & fair by neutral outside observers, which Muzorewa won. Unfortunately that wasn't good enough for the UN and Afrocentrist leaders in the old British Empire like Julius Nyerere of Tanzania, who insisted on absolute majority rule with no stake whatsoever for the old white elite and no constraints on the militant ZANU & ZAPU; Carter, braindead dove on foreign policy that he was, was of course on board with their demands and Thatcher in turn proved in this case to be less of an iron lady & more of a jellyfish, to catastrophic consequences for Rhodesia/Zimbabwe and even one half of the guys who had rejected the Settlement's terms (the aforementioned ZAPU).
It must be understood that in the context of Rhodesian/Zimbabwean politics, 'majority rule' was going to translate to 'tyranny of the majority' and the massacre or expulsion of everyone in the way of said (Shona) majority. Mugabe made that inevitable and it's not at all likely that getting rid of him was going to also translate into getting rid of that Shona-supremacist majoritarianism at the heart of ZANU (it didn't even now BTW, Emmerson 'the Crocodile' Mnangagwa has just been treading water instead of meaningfully improving anything ever since he got rid of Mugabe, though he did also at least do the country a solid by preventing Mugabe's even worse wife Grace from taking over and shitting the place up further still). The Internal Settlement was the best realistic path forward for Zimbabwe and it's a crying shame that it was stillborn, as Zimbabwe-Rhodesia could have had the best of both worlds: a black government with white advisors who could have kept the infrastructure & farms going and actually wound down the race war instead of further escalating it into driving the white Rhodesians out of the country and decimating non-Shona black peoples, thus avoiding the famine & genocide Mugabe's reign of terror was best known for.