Colossus' %base health increase doesn't grant enough health and actually grants less total health the more health you have.

[snipufin]

I have a max level Abrams (without T2 Infernal Resilience because I'm not sure how that interacts with it), and without any extra items his base health is 2980. 15% of that is 447.

• Buying Colossus and a small green item of your choice (except Rebuttal since that also gives bonus health) gives you the 7.2k vitality investment, +300 bonus health and +15% base health for a total of 4715 health.
• If you replace the Colossus with Extra Health (+210), Radiant Regeneration (+90) and Diviner's Kevlar (or any 6.4k green item with no bonus health), you get the same 7.2k vitality investment and +300 bonus health for a grand total of 4442 health.

4715-4442 is only 273, ~9% of 2980.

However, let's keep testing:

• Buy the first 11 6.4k items from the Vitality store, and without too much math, you'll have maxed out vitality investment tree and a grand total of 5815 health.
• Now sell Colossus for Extra Health and Radiant Regeneration and you'll have 5619 health.

Now the health difference is somehow smaller at 196, ~6.6% of 2980. Somehow the math ain't mathing and I'd appreciate it if you gave the big boy item the justice it deserves.