There are lots of things that money could be spent on to benefit the area.
Each has a cost and each has a benefit. If a greater benefit can be derived from a similar cost by using the money elsewhere then it makes sense to do so.
Unfortunately of course, benefits are subjective. I happen to think that the TfL improvements to the centre of Brixton have improved things significantly. More space for pedestrians, no barrier in the middle of the road, a more direct route up the hill and less traffic thundering past Windrush Square, and a better Windrush square that is being used more than it used to be.
Maybe you don't happen to think these things are significant; perhaps I place more value on the quality of public space than you do.
It's fair enough to criticise the design of the scheme itself but once people just start saying something is "too expensive" without any idea of what this kind of work usually costs, or how the cost was distributed across the various elements of the scheme, or how much of it was money that would have had to be spent on road repairs and the like anyway, or how much alternative schemes like refurbing the rec centre would actually cost... it just seems a bit of a meaningless discussion to me. Just a kind of reactionary moaning really.
If someone were to say, well, the road/pavement improvements cost about £1M and the square itself cost £5M and it would cost £3M to refurb the Rec centre or £2M to refurb the indoor market, then don't you agree that that's a very different scenario to, say, one where the road/pavement improvements cost £3M and the square cost £2M and refurbing the rec centre would cost £9M and refurbing the indoor market would cost £6M?
Where has this £7M figure come from, anyway?
The TfL info says that Phase 3 (Windrush Sq and changes to traffic flow around St Matthews etc) was set to cost £4.25M. It's entirely possible there was a cost overrun but it would be good to see where these numbers are coming from.