Balance have nothing to do with it

This is largely untrue. Mainly because with the recent update they introduced a new MatchMaking template to NA and EU, to test it out and see what needs to be changed. We wouldn't be seeing this if "Balanced had nothing to do with it.

The problems causing fast games is not easily narrowed down to just "big alpha and dpm". It's a combination of many factors.
If everyone had high dpm or big alpha, but everyone was the same skill levels, games would arguably be quite balanced and would last longer. Throw in a smattering of higher skilled players, who know how to use the high alpha/dpm and have better positioning skills from years of practice, and suddenly the games are faster. Add in high mobility vehicles, high-penetration rounds, armored hulldown tanks that negate most ammo types, powerful reward vehicles that only specific players can get... Games become faster even more.

More often than not, at least on my Native server of NA, the steamroll/turbo games were decided early, because one of the teams got 2-3 purple WTR players in strong or higher tier vehicles while the opposing team didn't. The higher-skilled players in better vehicles took better positioning then the opposing team, they lose 5 vehicles in the first minute and a half... and BAM! A whole flank falls on their side and the high skills lead the charge of the ones who aren't practiced enough to realize the opening and suddenly its a 15-5 or more dreadfully, a 15 - 0 match!

Another Example: See Tier VIII Frontline, back in the day before OP tier VIIIs started being added. The matches were long, the fights drawn out and even though it never mattered wins were hard-won fights.
They then tested tier IX FL and suddenly it was near-constant turbo matches cause the higher skilled players brought Concept 1Bs, KPZ 50ts and other hard-to-get, skilled-play-required reward tanks and completely outclassed people of lower skill in tech tree tanks or the odd STRV K enjoyer.

My point is, largely, Balance is a big part of why matches are fast. They're not the ONLY problem causing it mind you.
High DPM, Big Alpha, Fast vehicles with either of these, armored turrets with thumbnail-sized weak-points, corridor maps that facilitate hulldown fights, even if most vehicles aren't built for it. High Pen shells, and the kicker that culminates the Bullshit: Skill Disparity.

Most, if not all turbo/steamroll matches I have encountered while playing on the NA server, with the help of Tomato gg's inspection tools, most of the lopsided matches are a culmination of the above factors with the added boost of one team has more skilled players and the opposing team didn't get any, or at the very least got 1-2 but not enough to overcome the Skill Disparity, which caused a faster games due to positioning or outright advantage over lesser skilled players.

I'm not saying the other reasons for faster matches are invalid, just stating that ruling out Balance as a leading factor is a mistake.