1) the departing plane not climbing like a bat out of hell, and
Yeah, but what constitutes "a bat out of hell"?
I just did the calculation for a PA28-161 (the only aircraft for which I have performance data to hand right now) and that aircraft can already reach 200' by the end of the runway, assuming ISA conditions, nil wind and MTOW. Lightly loaded and with a 20kt headwind, 300' by the end of the runway. And that aircraft is by no means a spirited climber.
Anything else with a lower weight or more powerful engine will be able to outclimb a PA28-161. Heck, I think even your TB would reach circuit height by the end of the runway if lightly loaded and flown with the most efficient climb profile. And that's not even considering the fact that the aircraft taking off might have been doing a T&G or go-around.
We're not talking about Extra-300, Pitts Special or RAF tornados take-off performance here. Quite a few relatively normal aircraft are able to reach circuit height by the end of a 1000m runway if the conditions are right.