You would basically be guaranteeing half of Jackson's contract if you did a 10 year deal. Based on his age, that seems like a reasonable timeline.
I realize the yearly cap #'s would look different but each season would be like $25 million guaranteed cash and $20 million in non-guaranteed cash.
Even if you only guaranteed like $150 million of the deal (in line with Mahomes contract) and still paid Jackson $45 million per year....how much of that contract are you likely to pay out? He's your franchise QB in his early 20's. So most of it? Even if he gets hurt and misses an entire season....your going to give him another season or two to try and return to form.
Kind of like how people always talk about how the Steelers typically pay out the full contract regardless of guarantees. Ravens have approached it in a similar manner over the years. So if you are going into the situation assuming you are paying the thing out...what's the big deal? Keep the engine that generates wins for your team happy.