Cant get Arthur to work

For your question, the 2245 hp build assuming no extra mitigations including and no enemy penetration:
physical EHP: 100%-100/(100+272)= 74% mitigation. 2245*174%= an pEHP of 3887.
Magical EHP: 100%-100/(100+208)= 68% mitigation. 2245*168%= an mEHP of 3761

The 3045 hp, no pen or extra mitigations
physical EHP: 100%-100/(100+107)= 52% mitigation. 3045*174%= an pEHP of 4619.
Magical EHP: 100%-100/(100+98)= 50% mitigation. 3045*150%= an mEHP of 4552.

So yes, at a first glance your EHP looks higher, but we're not factoring late game pen builds from your opponents (or Qin's Sais, Heartseeker or soul reaver damage).
Let's factor this in:
For a regular assassin build (which usually hits 30 OR 45 flat pen gonna use the 45 for the example)
a mage build with 30 flat and 30% at least.
an adc with exe stacked and titan's bane.

So your pEHP against an assassin:
For the 272 prot, the eHP becomes 3803. a loss of 83 ehp. Heartseeker will hit after mitigations for 42 damage (or 135 EHP)
For the 107 prot, the eHP becomes 4210. a loss of 409 hp. Heartseeker will hit after mitigations for 113 damage (or 183 EHP)

mEHP against magical
For the 208 prot, the eHP becomes 3371. a loss of 390 ehp. Soul Reaver will hit after mitigations for 45 damage (or 90 EHP)
For the 98 prot, the eHP becomes 3626. a loss of 926 hp. Soul Reaver will hit after mitigations for 173 damage (or 213 EHP)

pEHP against adc (used titan's bane 40% for the high prot and 15% for the low prot the high prot is actually less pen from TB than 40%)
For the 272 prot, the eHP becomes 3392. a loss of 495 ehp. Qin's Sais will hit after mitigations for 33 damage (or 67 EHP)
For the 107 prot, the eHP becomes 4165. a loss of 454 hp. Qin's Sais will hit after mitigations for 75 damage (or 152 EHP)

So in all cases, the EHP total is higher. The problem is that for every bit of pen you lose a lot of EHP in the second build. And on top of that, if someone has a life shredding item for every basic they will hit a lot harder. especially the difference in EHP for mages is going to hurt you a ton.