Raspberry Pi Zero W with an external WiFi dongle Edimax EW-7811UN running OpenWrt 18.06.4, the Pi spawns up an access point with it's internal WiFi and the external dongle is connected to the local WiFi, the traffic is routed between the interfaces.
I also have high ping time differences. The ping time on the Pi directly is about 30ms to baidu.cn and if I ping baidu.cn with my laptop (that is connected via the Pi to the internet) I have a least +30ms more ping time, maybe this is related to the full RX buffer.
The Realtek USB dongles are not very robust for AP use. Those with QCA chips are pretty rare and generally expensive on the used market (US$40, last I checked). For that or less you can buy a complete 2x2 2.4 GHz router with 16 MB NOR, 128 MB NAND, 128 MB RAM, two Ethernet, in a 2”x2” package from a reputable manufacturer. Half that without the NAND flash and a slower MTK SoC.
The GL.iNet GL-AR300M is, in my experience, a very good, Qualcomm-based, 2.4 GHz router with 100 Mbps Ethernet. It costs about US$40. At about half that price (US$20), there is the GL-MT300N-V2, though I have not tried its wireless and don't have any other experience with MediaTek wireless.
I haven't looked at the "cheap" 5 GHz devices in a lot of detail. You might get some ideas from the 300+ opinions at
That thread has been around for a while and some of the candidates from a year ago are no longer available, or have had some "unfortunate" changes in hardware without a model-designation change.
I do have a GL-iNet GL-AR750S which i think is a great travel router, but I believe there are less expensive units that meet your needs. Then again, at US$56 right now, if I didn't already have two, I'd probably be buying another as a spare. You still might be better off with a MIMO 5 GHz unit, as "cute" or compact as the Slate is.