McFeely/Markus seem to believe that removing Infinity Stones is what causes the timeline to splinter and Steve not having Infinity Stones leads to the BTF rules.
Anyway, the Russos have made it clear that any time travel, regardless of whether you remove Infinity Stones will cause an alternate timelines. Also, we just finished Loki's show and we saw alternate timelines being created without Infinity Stones. That should have put a nail in the 'Steve was always Peggy's husband' theories.