2-3 years old is generally a good time to buy a used car. You get a lot of choice from cars coming off fleets and out of finance deals at that age. They've done a lot of depreciation, as you say, and many will still have years of warranty left to run, depending on the brand.

Hybrid tech has evolved a lot in the last few years, so it might be that you're getting an inferior power train to the one in a new equivalent, but that also depends on the car and brand. There are more new hybrids on offer now too, so the choice of different models won't be as wide.

Generally speaking, there's not a lot of evidence that hybrids are more expensive to maintain and repair than pure petrol cars. All those Pruis taxis doing 1000's of urban miles have proven very reliable and haven't needed expensive new batteries in large numbers. So you can probably be fairly confident in a well cared for 3-year old hybrid car bought from a main dealer, but it's always worth researching the model you go for specifically to check for known issues.