When the Merge happened we started with 1-3 and 3-5 queues.
1.5 years later we’ve reached ±1 for every BR which is already very nice.
Which means we have a bif enough playerbase to continue fine tuning the MM brackets.
The next step should be ±0 for BR5 as this BR basically includes everything that would have been BR5, BR6 and BR7 – e.g. from MKB 42 to Me 262 and from Tiger E to Tiger 2.
Besides, BR4 to BR5 arguably represents the widest power gap:
Semi-auto rifles are simply not competitive against select fire rifles,
BR4 tanks usually have zero chance against BR5 end game tanks,
BR4 planes reportedly struggle a lot against jets.
Last but definitely not least, BR5 is full of weapons and vehicles that were not used in WW2 (AS, RD, Hyde, T20, Autohei, Su-9, HoRi, Rocket Pershing, etc.), and being sent to sci-fi land when you dare to equip a single SVT-40/G43 doesn’t feel nice or immersive at all.
(The following step after that in my opinion should be ±0 BR for BR1, because new players don’t deserve to be instantly thrown against T-28/Pz IV F1/APCs/Uragan/Fedorov 1912)