I disagree. I believe this is only true if you switch to +/- 0 and then don’t make any other adjustments. The reason tons of items are in a specific BR is because “well, what if they get up-tiered, then they’ll be weak, so let’s allow these couple of overpowered weapons into this lower tier just in case.” If you separate BRs and then re-classify weapons and vehicles knowing that they will only ever face the same BR, you won’t have lopsided nations per BR (ideally, if done correctly).
As far as matchmaking time, I’ve never waited more than 1 minute, and barely ever more than 40 seconds, in BR1-3. I don’t play 4 or 5, so couldn’t say, but the playerbase will definitely redistribute if +/- 0 is implemented, because there won’t be the up-tier boogeyman to contend with, and better balance means better distribution of nations and BRs.
Additionally, you could add an optional “willing to uptier” checkbox like the join any box, which would only engage after a certain amount of time (30s, 60s, whatever makes sense), and any TEAM, not just individual player, who has an imbalance of BRs gets 5% score multiplier per net discrepancy (so if one team has 1 lower tier player and the other has 3, they would get 10% score bonus for “fighting up hill”).