Unless you have run into bugs or have real needs for higher throughput, I would wait another half year or so for filogic devices that offer higher throughput to become more prevalent in the market or to choose another repeater device that offers 4t4r streams. The dap-x1860 is a 2t2r device and is limited in terms of throughput. It makes a lot of sense to choose the dap-x1860 if your equipment is older and you need to upgrade now, but it is not as future proof. Compared to the dap-x1860, the TPLink RE650 seems still quite good in terms of hardware capabilities and an "upgrade" may not really be worth it.
While the DAP-x1860 obviously can't compete against mt7622, filogic 830 or ipq807x devices with dedicated 4x4 radios for each band (even less in a router function, which admittedly isn't a real option with its single ethernet port), it can be a pretty capable 802.11ax AP (with a wired uplink/ backhaul) for a single room or in the perimeter (think garden coverage) where consistent top-performance with multiple connected clients might not be the primary requirement. Form factor, price(!) and features are a quite nice match and range is pretty good for this device class (compact wall-wart design with internal antennas).
If it could it be an upgrade for a RE650 is a bit more questionable, yes most clients will be 2x2 themselves (so you will see ~double the throughput with 802.11ax compared to 802.11ac), but when it comes to servicing many concurrent client devices, difficult signal paths in a crowded environment with multiple small rooms/ corners and corridors, the 4x4 802.11ac radio in the RE650 probably retains the upper hand. If you're looking to service your entire house with one AP, I would recommend a more full-featured 4x4 device instead - but it can be a great addition (or be part of a 'whole fleet of wired dap-x1860' to get best wireless performance into 'every' room).