An intriguing statement, is this in fact correct? So if we ignore specialized builds and just assume some old normal grappler, we can assume a big strength and just athletics proficiency. no expertise, no other athletics bonuses.Actually for non specialized builds it is buffed.
So we have at the high levels we are debating:
5 (str) + 6 (athletics prof) vs Monster Athletics or Acrobatics
against
Monster Str / Dex Save vs DC 19
So now let me look at some of the monsters my party has grappled in game, and see if this holds up. I'm going to use sims since I'm going to be lazy and not do proper math

Note: A reminder that for this opposed roll, a tie actually favors the monster, because a tie in an opposed check "keeps the status quo" which is not grappled.
- Pit Fiend - Old
- Old: d20 + 11 vs d20 + 8 - 62%
- New: d20 + 8 vs DC 19 - 50%
- Lich - Old
- Old: d20 + 11 vs d20 + 3: 80%
- New: d20 + 3 vs DC 19: 75%
- Mummy Lord - Old
- Old: d20 + 11 vs d20 + 4: 77%
- New: d20 + 4 vs DC 19: 70%
- Iron Golem - Old
- Old: d20 + 11 vs d20 + 9: 57%
- New: d20 + 9 vs DC 19: 45%
So yeah just with my quick browse the old system was definitely easier for grappling in general. Its also notable that the harder it is to grapple a target in general (aka high strength or dex).... the more benefit the old system had. Its just the nature of opposed rolls vs a saving throw, when you have an advantage in an opposed roll it tends to magnify.