Last chapter's TBB was far larger than Flash Bijuu Dama because it was likely amped by Rikudo's chakra/other Bijuu chakra's combining.
-Look at the lake, about 2-3 mountains in length [
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]
-Look at all the Bijuu Damas combined now [
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], Kurama's is only half of that explosion. Compare it to the same water which was 3 mountains long, it's really not that much larger width wise, much greater height wise though.
-Now look at the lake of current chapter's [
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], it's at least 4-5 mountains long.
-Look at the statues dwarfing these massive mountains in height in that same scan, assuming the statues were on ground level. Now look at Sasuke's legged Susano atop of these statues and how small it is [
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].
-Now look at current chapter's explosion, it occurred atop of the lake, and completely dwarfed it. Look at the mountains, they are so small it looks like they are in mountain ranged form [
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-Look at how high it is compared to the river splitting were the statues are, which are much larger than mountains height wise, it's completely dwarfed by its height.
Imo, this explosion is portrayed as far larger no matter how you look at it, lake, mountains and the explosion itself all add up to make it look much larger. Only reason the other one is seemingly bigger at first sight is because the mountains seem much larger.