Don't buy that one bit.. Are you telling me that we cannot play with Kane and Benteke upfront against the likes of WBA, Bournemouth, Norwich etc, without retaining solidity?
If it were that simple I'd expect to see 2 up front far more often than we do in the top echelons of football. After all, we're all West Broms to the likes of Chelsea.
We probably could play 2 up front and win - that still doesn't make it the most likely method to consistently end in a win for us (name of the game when it comes to league progression).
The only "gaps in midfield we'd be leaving" will be those available on the counterattack if we play the Masaleb combo because - while they have some magnificent offensive qualities - neither of them has the mindset of a defensive midfielder and therefore are instinctively inadequate to spot those gaps and position themselves to close them. Ergo, a proper DM who can do that job.
Even with a top DM (one that we would be unlikely to attract) with everyone else playing some kind of 4231 variant we'd be overrun. That's kind of the point of the formation - even with worse players you can overrun a 2 man midfield whilst keeping some attacking threat.
I agree that our mix of personnel isn't quite right, but that has nothing to do with how many we're playing up front and everything to do with playing two young, more attacking than a DM midfielders.
The best way to reduce the chance of your opponent scoring from a set piece is to reduce the number of dangerous set pieces you give away. Partly that's a personnel issue, but mainly it's a matter of playing a style and formation that has a lot of possession and presses high up the pitch.The other major threat from these smash and grab teams are set pieces - where Benteke would be as good as having an additional centre half.