Believe me I`m aware since I`m using alu pushrods on all my engines and they are FAT

So what happens if you add a breather line to your valve covers you think? Do you think that will help the oil escape through the push rod tubes? I believe not, the oil will instead follow the path of least resistance which is now your "breather" line. A breather line full of oil is not a breather line.

The best breather box or vacuum pump in the world would not help if you have excess pressure due to leak down.

But hey, breathing from the valve covers has been the way for the last 40 years or so..

-BB-

It's Horses for courses, there is no one size fits all, track cars that see corners on most r.h circuits can fill the LH valve cover with oil, under some conditions with wet sump motors on very long sweepers with high revs in top gear it can lift the valve cover with bad things happening to the LH rear tyre, dangerous, not to mention the hallowed race track doused in oil, venting the valve cover into the mandatory breather system is neccasary in thus case, even my dry sump motors have this venting on both sides, tho dry sump scavenging of the left head is the ultimate, bail clips need to be very strong to contains pumped up cornering oil, as well as being flagged off the track, a lost motor is no fun and expensive. Vent the rocker chambers for racing, preferably scavenge them back to the DS pump.
It's also possible to suck the RC gaskets IN, again massive oil leaks will result, i always fully prepare valve covers to prevent it, tags are welded in to prevent the gaskets moving inboard ala Porsche, venting helps with this also.

Build the engine properly and there is minimal blow-by ;)

Venting from the rocker covers and not the case MAY reduce oil drain-back to the sump

As above, Blow by isn't the cause, it's pure centrifugal forces, both from oil sling and slick tyre corner forces, sure enough, Any motor with blow by advisably should not be racing on the long circuits anyway, it won't last the race.