There is a drop, 15-20%, depending on card, but I'd still use eGPU. For me, its most important advantage is that it frees your laptop GPU so CPU has all the thermal room possible. The he desktop equivalents are faster, so even factoring the TB3 drop it still will be faster than on board solution or at least equal. And you can upgrade the eGPU later, it's worth keeping regardless of how powerful internal GPU you will end up getting..