You are new to engine dynamics by the sounds of this there are many factors that give a two valve head a performance advantage at a cost ratio to four valve head. Yes four valve heads can flow higher numbers but cost a whole lot more to build think about it I am going to use bigger valves so I only need half as many and so on down the valve chain. I'll edit in some other facts soon.
Quoted " You can't beat the quench & flame travel characteristics of a good 2V head, nor can you beat the pressure recovery characteristics & efficient discharge coefficient than can be achieved.
4V only have the curtain area advantage, other than that they are inferior in every way.
That curtain area advantage is a big one tho & makes up for the other shortcomings at higher rpm.
Bet most people don't realise the curtain area advantage is not as big as it looks on paper tho - valve to valve shrouding reduces the effective curtain quite a lot & the necessary placement of the valves requires more valve/bore shrouding as well, also direct acting cam on bucket setups are significantly lift limited compared to rocker arm setups.
A canted 2V head can place the valves away from the cylinder wall so that the curtain area available can be almost fully utilised with fairly even discharge around the whole circumfrence of the valve - that makes for a very efficient intake tract with little or no 'wasted' volume. Compare that to a 4V head with it's shrouded valves, which must have port/bowl area above them even in areas that are innactive - resulting in less efficient use of the port volume, lower pulse tuning 'signal' & lower velocity ram effect.
In short - a well developed 2V head can outperform a 4V head up to the point where curtain area becomes the restriction in the 2V head, from there the 4V will outperform.
Oh yeah, you also have excessive pullover & reversion on 4V heads - by their very nature low lift flow is good, too good in many cases, something that flows well in one direction usually flows quite well in the other direction, so at lower rpm 4V engines experience higher rates of reversion (that's why they are doughy down low, got nothing to do with big ports).
They also waste more potential trapped VE out the exhaust as that high low lift flow comes into effect at higher rpm during the overlap period."
Also with the ve-volumetric efficiency you do realise that the scavenge effect can draw air through the intake faster it is called induced exhaust sometimes. This is the whole Idea of using tuned extractors so the crate a scavenge which will induce air flow.
Do you even know that compression increases with rpm it is called dynamic compression this is what I mean by you don't understand the dynamics of a engine, you just quote paper figures.