More than the multipliers, I like the tier thing with all the transformation having a similar gap(before discovering the 50/2/4 on neoseeker I thought it was 50/50/50). The mssj destroyed the x50 for me.
If for goku, Gotenks ssj pre is ssj3 adult tier, base Gotenks for me is ssj2 adult tier. I like the ((a+b)+2 tiers) for the fusion. The a+b making them closer to or stronger than the adult.
For post base Gotenks, I'd put him half a tier higher than pre base. He is closer to fat boo but still far from super buu that is why he looks hopefully strong enough for piccolo. But it'is not fat boo unfortunately.