Winning a slam without dropping a set (logically) makes one much better than winning a slam being on the verge of losing multiple times. So yes it is 100% true.
While that's true winning a Slam in a dominant fashion is considered more impressive than winning a Slam saving match point(s), your attempt of discredit Serena's Slam wins won't be successful, since Serena has showed she was able to dominate Slams several times, so the "comeback", while it's not a record, only adding to legacy as an important and valuable traits of a Champion : mental toughness.
Just like every Slam win is different, you can't compare Serena's Slam win in modern days with Slam wins in the past where the competition was poor. Different fields, different difficulty in winning. The first ever Wimbledon winner just won a Slam in their backyard against a " circus of friends". You would bet they are not even to be qualifiers if they were competing in modern days. Just like you can't compare Slam wins with ITF wins nowadays.
Only if all the 4 Slams set up 7 robots ( at an increasing difficult levels after each round) there to play tennis where 7 robots has the same strength, the same tennis skills and smartness and players to win Slams have to beat the same 7 robots every time when they win Slams. Yes, only when it set up like that then you could compare and say all Slams are equal. Until then, as most knowledge people ( Evert, Jon Weitherm, Mc Enroe, Kim, Davenport, etc...) already conceded, Serena's Slam wins is second to none in term of achievements and greatness. ( I would take Jon W's words over lots of people, esp jealous posters here. Just read some of his column and asked yourself whether you are able to write that before calling him " Jon Worthless". )