They don't need to be especially backloaded if those are the only things of particular note that they do.
When you start considering all of the other moving parts of lesser or greater note then it becomes an issue. Passing on Bulaga, letting Clark play on the 5th. year option, not extending any of next years free agents would be the larger issues. Crosby-like or lesser signings start to add up.
Anyway, I doubt they're going go spring for a high ticket ILB, Littleton or anybody else. Bringing in Kirksey for a look see I would take as a tell, Gutekunst looking for a moneyball move in a player unfairly discounted by his injury history. I imagine his medicals will be the main focus of the evaluation given his hamstring (2018) and seaon ending pectoral (2019) injuries. They may not like what they see in Kirksey when they get down to brass tacks, but it is an indication of where they would prefer to go, a vet to call the signals paired with a rookie without spending much cap (but perhaps a Day 1 or 2 pick) at the position.
Going all-in for one season rarely works out. Acting blind to what comes next amounts to a wing and prayer. And when it does not work out there is high price to pay.
Either you have to rebuild (last year's FA haul) or you have a winning core you are looking to compliment, but manufacturing a winner by spending to the hilt in free agency with backloaded contracts or trading away a bunch of future high picks for stars is a mugs game. The Packers are in a pretty good place with big strides forward last season.
A lot depends on what the revenue projections are for 2021 and beyond. If a big cap jump is expected staring next year with the CBA and LA and Las Vegas stadium completions, something about which we have little to no visibility, it could look like all-in when in fact it is not until we get further down the road.