Production costs in Civ6 are lower than in Civ5. I played a few games of them back-to-back. In the starting turns in Civ5 you produce units in 8-15 turns, in Civ6 I'm producing units in 4-8 turns.
Production costs (for comparable buildings and units) are higher in civ 6, not lower.
However, base yields from terrain in civ 6 is also higher, improved terrain yields are higher, and these factors somewhat balance the higher base costs in civ 6.
I suspect that the devs balanced around this, which seems to work out roughly well if you consider tile yield power creep in civ 6.
What breaks civ 6 however, and what I feel is what the devs overlooked when they balanced around higher production costs, is that there are numerous ways to boost production per city to levels
much higher than civ 5 offer.
Examples of this is abusing early Work Ethic in 6, trade routes being more powerful in 6 (civ 5 number of routes is much more restricted, exporting production requires a Workshop, while exporting production prevent you from exporting food or trading for gold whereas civ 6 can give you all at once, and more often), the Industrial Zone (and partially Harbour) offers ludicrous amounts amounts of production in a myriad of ways (base yields, adjacencies, buildings, envoy bonuses to said buildings, regional effects, regional effects and buildings boosted by great engineers), % based production policy cards, and good old Magnus chopping.
Plus that you can faith and gold purchase a lot more in civ 6, which frees up additional production indirectly.
All these combined (and probably many additional factors I didnt mention here) severely power creep production times in civ 6 compared to civ 5, despite production costs being lower in 5.
And production is not the only victim of this, the same is true for Science, Culture, Gold and Faith as well.
This breaks the late game to the point where total yields just tend to
explode around the Renaissance/Industrial era, where games are over shortly after if you care to somewhat min-max these things.
This is currently my biggest pet peeve with civ 6, and why I've been playing a bit of civ 5 again recently - the lack of a late game in civ 6.
The pacing of the game is just much, much better in 5 compared 6, even if the game otherwise has its flaws as well.