Alienware m15 R2 is limited to 16 GB of RAM or just half of the cheaper Dell G7 15 7590
Most OEMs have at least three classes of gaming laptops: budget, mid-range, and flagship. If you want the fastest there is, your instinct would be to look at the flagship lineup as it should offer more powerful specifications than the budget or mid-range options. In Dell's case, however, the mid-range models carry most of the same CPU and GPU options than the higher-end flagship models while costing less.
The systems of interest here are the mid-range Dell G7 15 7590 and the flagship Alienware m15 R2. The former can be configured with the same octa-core Core i9-9880H CPU, GeForce RTX 2080 Max-Q, and 4K UHD OLED display as found on the Alienware equivalent. In fact, its two upgradeable RAM slots allow for a maximum of 32 GB as opposed to just 16 GB of soldered RAM on the Alienware m15 R2. It's not common for a lower tier model to have an upper hand in a particular specification like this. (G7 15 i7-9750H, RTX 2060 on sale now at Amazon)
The Alienware m15 R2 still offers more features than the cheaper G7 17 7590 outside of core specifications including a sleeker chassis design, per-key RGB lighting, and Tobii eye-tracking. Dell is also promising 32 GB RAM options for the Alienware m15 R2 in the near future. The core gaming experience and internal hardware options, however, are otherwise almost the same between them despite the "flagship" status of the Alienware name.