That's the point: that _is_ 55-60% of RFA's BTGs, BUT, most are down to 4-6 APCs, 2-4 MBTs, and 2-3…
Thus, that with 'such a concentration of power' is relative: actually, 3-5 BTGs have the strenght of what one BTG should have. So…
That's the point: that _is_ 55-60% of RFA's BTGs, BUT, most are down to 4-6 APCs, 2-4 MBTs, and 2-3 companies of 15-20 troops each.
Thus, that with 'such a concentration of power' is relative: actually, 3-5 BTGs have the strenght of what one BTG should have. So, actually, even if they have, say, 90 BTGs in all of Ukraine, their actual total strenght is that of about 30 BTGs.
The 'most complete' units right now are those in Kherson and southern Zaporizhzhya: these are at 50-70% of their nominal strength.
All that's meanwhile keeping the Russian frontlines together is their artillery.