if the western fron is too strong they're diverting from the eastern front to incrase defences there, slowing the british and american progress down and increasing the soviet progress.
the soviets and the allies are meeting west of berlin, no matter what.
Not necessarily, actually - put it this way. Assuming that the invasion takes place as if like OTL, but in 1943 - and there's the historical German forces in France
in 1943 to resist it.
That's only one or two divisions.
The Western Front promptly collapses, and if they're lucky the Germans can pull together enough forces from Italy or the Eastern Front to stabilize the situation on the Rhine.
If they're not lucky (and that's a possibility), then the Western Allies wreck the logistic support capability of the Reich by closing up the Rhine and wrecking the Ruhr's capacity to provide weapons of war to the Axis.
Either way, once things stabilize, the Western Allies are a few hundred miles from Berlin. The Soviets are much further - an entire summer offensive further away from Berlin than they were in OTL Jan 1945, even assuming they get Bagration-like success in 1943. And there's no one offensive in the second world war that can clear as much ground as the Soviets have to cover - simple logistics dictates they
must use two offensive stages to get that far, even against ineffectual resistance, because they need to redeploy supplies forward and so on. An offensive can't just rumble forward at maximum speed for several hundred miles - and the Soviets are one more offensive push away from Berlin than the WAllies are, in this scenario.
As such,
if the Western Allies want Berlin, they can get it.
