As a manager and I can tell you that the push back to estimates is primarily from engineers and cheap company owners ("why spend time estimating when I/they can code?"). Estimating, wire framing, documenting, manual testing, security testing, etc are all hard but necessary.
If you don't schedule time to estimate, the estimates are worthless. Rule of thumb, anything that can be done by one engineer in less than 1 month should take about 1 day to estimate, anything under 3 months, one week, anything longer should take up to a sprint (2 weeks). As a manager with experience, you should roughly know what level of time needs to be spent by your team planning their work prior to executing. Chances are, in the estimation work, the engineer(s) will discover questions that have not been answered by the product specification that need clarification. And that's the whole point: getting as clear of a picture as possible.
As for any manager that thinks they can squeeze value is naive about what software engineering is. This is not a manufacturing line.
Well, yes. Estimation is design. Only if you call it "estimation" the engineer who's been berated into crunch-overtime for a miss in the past won't want to do it and will do it badly when forced, and the cheap company owner whose own behaviours drive teams to estimate badly ("that estimate's huge, I'm not paying that, estimate it again but smaller") won't have had good experiences to understand why that design phase is valuable.
There needs to be enough time in the schedule to design to an adequate level for the problem at hand. You don't necessarily want as clear a picture as possible, but you do want as clear a picture as necessary.
If you don't schedule time to estimate, the estimates are worthless. Rule of thumb, anything that can be done by one engineer in less than 1 month should take about 1 day to estimate, anything under 3 months, one week, anything longer should take up to a sprint (2 weeks). As a manager with experience, you should roughly know what level of time needs to be spent by your team planning their work prior to executing. Chances are, in the estimation work, the engineer(s) will discover questions that have not been answered by the product specification that need clarification. And that's the whole point: getting as clear of a picture as possible.
As for any manager that thinks they can squeeze value is naive about what software engineering is. This is not a manufacturing line.