As Gaijin seem to have forgotten about prop balancing, I would like to make a number of proposals, starting with the Yak fighters.
As you most likely already know, most Yaks are incredibly strong at their respective BRs, but I believe several of them should have their BRs increased.
First of all, the Yak-3e and Yak-3 are quite undertiered, and I would propose sending both of them to 4.7 at the very minimum, and possibly to 5.0 if Gaijin are feeling generous. I propose 5.0 as an upper limit on the basis that the 3P is still perfectly competent at that rating without feeling overpowered. What it gains in stopping power, it loses in a slight augmentation of mass, so I think having all of the derivatives of the Yak-3 at 5.0 would be fair, due to the fact that they would effectively become sidegrades.
The next Yak I would propose to be moved up to 5.0 is the Yak-9U. Again, incredibly strong at its BR, the VK-107 is an absolutely monstrous powerplant (but less ergonomic to play than the Yak-3 as it does require MEC to maximise its potential), and some of the less meta planes at that BR could benefit from seeing the 9U a little less often.
Finally, in the most egregious case of a Yak being undertiered, there is the Yak-3U, at the lowly rating of 5.7. While I understand its placement may be a reflection of ShVak cannons (and by extension B-20s) in the past being a shadow of what they are currently, it is time for Gaijin to take stock of the situation and deal with it accordingly. Something like a Bf-109 K-4 (more on the later 109s in a bit) cannot hope to win against a Yak-3U pilot who is even halfway towards being competent, and as they inhabit the exact same BR, this is a clear example of a failed attempt at balance (if, indeed, there ever was an attempt in the first place). As the 3U is almost perfectly tailored for the current lower-altitude Air RB meta, putting it at 6.3 or even 6.7 would not hinder its performance significantly.
Another plane I would propose to move up is the Spitfire LF IX. Like the 3U, it is almost a bespoke fit for the current air RB meta, and only really falls short on the grounds of its straightline speed not being exceptional. I believe anywhere between 6.0 and 6.7 would be fine for it.
I promised to mention the later Bf-109s (namely the G-6, G-10, G-14, and G-14AS). As they are effectively sidegrades of one another, with the major differences being which altitude their engines are tuned for, I believe all of the late Gustav variants of the 109 would be perfectly fine at 5.0. The K-4, in the ideal world, would stay at 5.7, but if the more oppressive planes at its BR do not move, perhaps taking the K-4 to 5.3 would alleviate some of its shortcomings.
Also send the BI to 7.3 I hate that thing with a passion.