Issue is: Changing at London Bridge is not a very desirable one given that the vertical distance between platform and concourse is so high. Change at Lewisham involve much shorter walk and less steps involved.It has been extensively discussed upthread (or se0arately, or both?).
I don't recall your specific point being made, though.
My guess is that most passengers will change at London Br, and a fair number of Bexleyheath Line passengers will simply switch to Victoria.
Those who are heading to places within walking distance of CHX/WAE will split between the CST and VIC services so some will opt to change platforms at Lewisham. Not sure it will be vast numbers.
Changing at London Bridge is worse than Lewisham, as Bexleyheath Line will still only have 2 tph to London Bridge while Lewisham get 4tph. Should the Victoria service also goes to Cannon Street, as per the pre 2019 plan, then a London Bridge change shall be more feasible.
The current timetable is a half baked solution to the 2019 proposal, which actually have more passenger disbenefit than benefits. It is especially true for late night services after 9, which CHX service is often fully seated from Waterloo East all the way upto Eltham.
Meanwhile, changing from Charing Cross to Cannon Street do add 3 minutes to the journey time as calling at 2 more stations. Google Map and National Rail journey planner suggested Lewisham as the preferred interchange point.