Like him or not, that's totally different from the situation with Trump and Tom Steyer when they announced their candidacies. So, I think it's wrong to compare the situations of all three as the same.
That said, I think it's a bad idea for him to run. It just reeks too much of a sense of entitlement, staying out of the race for a year and then jumping in after the battle. And without much of a cry for his participation. And sort of weird to start in Alabama, hardly the hot bed for East Coast politicians.
Keep in mind that when another New York City mayor, Rudy Giuliani, ran for president, he was pretty famous across the country for supposedly being "America's Mayor," and held off entering the GOP primaries early, putting his hopes on Florida -- where likely a lot of Jewish retirees from around the country lived, where a lot of New Yorkers moved to, and is a touch more balanced politically than Alabama. And he got crushed and pretty soon after dropped out of the race. Certainly Michael Bloomberg has the personal finances to stick around as long as he wants, but it's a telling lesson of history that shouldn't be ignored.
I actually like things about Michael Bloomberg, not everything. And I don't think it's necessary for someone to get in the race early. Jumping in whenever one wants is perfectly fine, since you know the risks. And he does have solid experience in politics -- though I don't think being mayor of any city, even New York, inherently qualifies one for being President of the United States, even if you were a good manager. (Including if you were a good mayor of South Bend, Indiana.)
But still, it might have been more interesting to watch his campaign if he'd started a year ago. Mainly, I'm just not sure why he's starting now and in Alabama -- not that it matters if I know. But it's still a question worth pondering. Is it because he senses Joe Biden won't be able to carry the moderate banner to the finish line? Is he concerned that Elizabeth Warren is doing too well and is too much a progressive risk for the party? Has he just had a presidential bug for too long and thinks that at 77 this is his last opportunity? (I've also read some suggestions that he might feel she is too much a progressive risk for billionaires, though that doesn't strike me as Bloomberg kind of position.)
I don't know. The only thing I do know is that it's a bit weird to me that he's decided at this late date to run and to begin in Alabama, all at the age of 77 (actually, 78 by the time of the primary) without a groundswell of support. And while he began as a Democrat, he first ran for mayor as a Republican, then switched to Independent during his time in office, and a couple years ago returned to the Democratic Party. None of that doesn't mean he shouldn't run. Just that it all seems a bit weird.
Of course, it seems utterly ludicrous when another billionaire, Trump, announced he was running. Though Bloomberg is no Trump -- which is a very, very good thing. But Trump started early and built up support and ultimately ran a steamroller over all his opponents, thanks to an acquiescent Republican base. And that's not 2020 in the Democratic Party.
We'll see. It's odd. And a very uphill battle. But he's a serious guy, so I don't see this as an "unnecessary distraction" in the race. And if other candidates and their supporters don't like him running, then all they have to do is beat him.
But again, whether one likes Michael Bloomberg or doesn't, he shouldn't be put aside as just another billionaire who simply wants to jump from businessman to Make Me President. He's put in the work. So, he's a serious candidate. But it's still weird.