This 3 engine landing failed for the centre core, which is why it was lost. Specifically, there wasn't enough 'lighter fluid' to relight all 3 engines required, only one engine was lit. Thus the booster tried a 3-engine landing on a single engine, and hit the water at 300mph IIRC.
They powered up the centre engine, then lit two engines either side of it, but then turned those off a few seconds before landing and still actually landed on a single engine for the last ten seconds or so. It’s hard to be sure exactly because the telephoto footage of the booster catches the start of the burns but misses the side engines shutting down. But when it pans back on to the engines, it’s clear only one of them is still lit (with one other flaring off some unspent fuel). That’s a very precise and tuneable thrust curve you wouldn’t be able to do with one bigger engine.
Interesting about the final part of the landing occurring with a single engine even with a 3 engine landing. Makes me wonder why they don't do something like 9 engines for the breaking burn and then switch to a single engine for the landing part. It might just be that is their final plan but 3 is easier to test than 9.
I know the F9 engines can’t throttle down to a hover, even on a single engine with the fuel tanks mostly empty, but I’m sure they did all their landings up until the last few on a single engine that throttled down to its lowest setting for a reason. Controllability matters and while max power suicide burns are theoretically ideal in practice landing at full thrust on all engines would be highly unlikely to ever be workable. If F9 had say 3 larger engines, I doubt landing would be possible at all. Also you need to be able to build a configuration with an engine in the middle.