This is such small market mentality. The Chicago Cubs should, every year, run a salary next to, if not a bit above the LT. The LT is something that is getting larger each year. Now, there's some CBT stuff that's going to go down shortly again, but I think it's probably safe to assume that the LT ain't going backwards. Add in inflation, and we have story, after story, after story where within 2-3 years many of these mega deals are all of a sudden not that big. For example, remember when people were surprised about Corey Seager coming in above market projections? He currently sits 21st in baseball, It's taken two years for six contracts to sign above him, and will likely continue to move down the pecking order. By next year alone he could be outside of the top-25. Bryce Harper was another story - he's been almost a bargain when you see where he currently sits in AAV (outside of the top-30 already) What it mans is as time goes, the contract, even if it feels big now, will become a smaller and smaller fraction to the LT and compared to his peers.
The point I'm making is this: Kyle Tucker doesn't have to be a 5+ win player every year with the further increase in contracts, the adding to the LT.... We also know that contracts have surplus value up front (at $40m, you'd be paying him for under five wins - wins are going around $9m+ on the market). So you pay more later, but inflation and the LT helps balance that loss out, as well.
Lastly, Tucker has a pretty great skillset. He's got a great approach (a skill that ages well) and is not overly reliant on his athleticism. He's capable of moving off RF down the road, and could play 1b as he ages (and his bat will likely play okay).
Is there risk? Sure. There's risk. There's literally risk getting in your car every day, there's risk getting out of bed, there's going to be risk signing someone to a 10-12 year deal. However, the risk here is the right risk. Just sign Kyle Tucker. Not only can the Cubs afford it, he's a really good player and a good bet to age well. There shouldn't be much of a debate here. If there is, you'll literally never sign a large contract. Ever. There is no such thing as a perfect player or a perfect contract. But Kyle Tucker is about as safe of a long term deal as you're going to find.