I have to agree with you, the team could be significantly strengthened with some pace, no doubt about it.
I often wonder if we all look at this backwards though - consider the key players we have sold in recent years: Maguire, Murphy, Adams. They have all been sold for around the same price, I don't know the exact figures, but the cost to keep these 3 players would take up a large percentage of our FFP. If we say (hypothetically) that these 3 players took 1.5m to 2m quid per year to keep between them, that could account for 20-35% of the wage bill. That could be suicidal if promotion is not gained considering that the club makes around a 4m quid loss every season without these players.
Of course there are the cup runs which can affect the turnover and as we both say, other ways to increase the turnover to boost our FFP, but having a squad of 25 players its easy to see why we wouldn't keep these 3 mentioned players - especially considering the dross we have bought on big wages that CW is having to either pay up or move on.