I dont see how a complaint message will help. It's not going to make your next flight more on time and it doesnt mean more time in bed either.

any delays cost BA money so they will be as keen as you are to avoid them so it's not a case of "oh well, given no one is complaining, let's just be a bit slack here....".

one of those things though I guess if it's a regular occurance, you could ask what they are doing about e.g. shortage of a/c (if that's causing it) and/or vote with feet and use someone else or use LHR or LGW instead.

I personally find LCY to be pretty good in terms of 'on time' performance not least because there aren't the "we have to wait for stairs / tracktor / tug / etc" or "it's very busy time of day...." reasons.

weather is an issue though.