I think increasing the keshik’s attack range to 1 (like the steppe lancer) would fit perfectly with their civilization’s theme and the unit’s design, increase it’s utility, incentivize more diverse army compositions, allow them to more effectively use their gold generation trait, give them more opportunity to utilize their civilization’s elevation bonus, and provide Tatars a minor buff that could help improve their effectiveness on more maps.
Theme wise, it would give the Keshik an identity of being a UU version of the Steppe Lancer; similar to how the Mongols and Cumans have UU cavalry archers. It would also help differentiate the Keshik from other cavalry units. Being a lance wielding unit, the extra range also fits the unit’s theme.
The extra range would allow the unit to position itself behind other cavalry units, allowing for more strategic army compositions with the Keshik occupying the second level of the formation and cavalry archers in the back. Front line options could consist of a Hussar meat shield, anti-cavalry camels, or heavy hitting knights. Being on the second level of the formation would provide Keshiks more time for them to utilize their economic trait due to longer lifespans during battle. It would also help with positioning when engaging on hills so that more Tatar units could utilize their civilization’s elevation bonus at once. If a castle isn’t available, the steppe lancer could replace the Keshiks; similar to how cavalry archers replace mangudai and kipchacks.
Edit: I should add that some other aspects of the Keshik would need to be altered for balance purposes. Specifically, their cost and training time would be increased slightly (perhaps to 65 food, 50 gold and 16 seconds elite training time), with reduced hp (130 with bloodlines) since they no longer necessarily a front line cavalry unit. They’d still overall be an above average unit since they’d require a castle to make them, and thus be a little harder to mass.