I think both teams simultaneously did well and also took huge risks with this move, if that makes sense.
Montreal unquestionably won this trade in terms of value. Drouin also significantly helps their offense, which was their death against the Rangers. However, unless Drouin learns to play center (or they move Galchenyuk+ for a center, which may be tough without having Sergachev as a trade chip?) they're still incredibly weak down the middle and they're not winning a Cup that way. The problem is that they have to go for it; Weber's not getting any younger, Patches is currently cheap but won't remain that way, Price isn't signed long term yet and their prospect pool sans Sergachev is mediocre at best/downright terrible at the worst. If they can address the center situation elsewhere, they're going to be a Cup contender next year. Otherwise, I'd argue they're still a pretender, which may be wishful thinking so take that into consideration.
Tampa got hosed value-wise here, which is why I think they're also taking a risk. However, they couldn't have afforded that contract that Montreal offered (not that I think it's a bad deal for Montreal, I think it's a calculated risk and I bet the contract will pay off for them) and needed more long-term defensive answers. Sergachev is just a prospect, and he's not worth as much as Drouin in a vacuum, but he's a good one with high potential. This will also help Tampa in the expansion draft, but they still need LV/someone else to take that Killorn contract IMO since Callahan (if he doesn't have a NMC, which I don't remember so someone can hopefully help me with this) is a pipe dream.
I understand the deal from both ends but it's a risk from both ends too.