The presence of Hyper-Threading for the Core i5 series has allowed the 65 W i5-8305G to perform much more closely to the 65 W i7-8705G. This is in stark contrast to the older 45 W i5-7300HQ where the 45 W i7-7700HQ and even the 15 W i7-8550U can outperform it in multi-threaded workloads. Shoppers now have one less reason to buy the more expensive i7 over the i5.
https://www.notebookcheck.net/The-Kaby-Lake-G-Core-i7-8705G-offers-no-substantial-benefits-over-the-Core-i5-8305G.302940.0.html
imo, judging by the core number it's quite pointless to compare intel G series to last year HQ series. The G series is intended to follow U series core segmentation. Both G and U series have the same 4 core / 8 thread at the i7 and i5 line-up, while H series (the real HQ series replacement) have 4 core / 8 thread in the i5 line-up and 6/12 in the i7. Both H and HQ series offers a significant upgrade from i5 to i7 while U and G aren't. Last gen U series (ex : i7-7500u) is also offering not significant upgrade between i5 and i7 because both are 2/4.
The problem with the i5 version is not the performance. You can only get it with 8GB of RAM and the RAM is not upgradable. Buying a laptop with fixed 8GB of ram with this price is a huge mistake. Even if you don't feel the problem today you will next year and I do believe people buy something like this to use it for a few years. I think it is an obvious (greedy) mistake from dell that did not put 16GB RAM as minimum when it is not upgradable. The price of this laptop is very high and it is only affordable for a lot of people to buy the cheapest i5 model so that is why they try to promote this model as being as good as the i7 model without mentioning the RAM and notebookcheck helping this promotion seems kind of sketchy for me.