In Patch 10.2, BG maps are receiving a major change that limit their use, but Mythic Neltharion is receiving some compensation nerfs.
Map Overlays are receiving one major change in Patch 10.2 that makes them much harder to use effectively — the arrow for the player is removed during dungeon/raid combat. This means that you won't be able to see your live location on the map, making it much harder to use effectively. No more GPS!
Of course, this would make Mythic Neltharion much harder since the vast majority of guilds are using Map weakauras to direct their raiders for the mechanics. Players should still be able to see the maps and use them as a reference for where they need to run, but unfortunately, will not see their position on the map. For those who were relying on using the Map Overlay as a GPS, this fight will be much harder for you now.
However, Phase 3 had some significant changes.
This means that players have more time to get into a safe zone, and players are able to get into a safe zone early to not lose damage. Theoretically, this should lower the DPS check of the encounter as well since Neltharion will spend ~24 more seconds casting and players will be able to do full damage while hiding.
A note though, the damage taken while standing in a safe zone wasn't changed meaning you'll still be taking a decent chunk of damage if you go in super early. Some guilds may use the new ping system to ping portals ahead of time and still go in last minute to reduce damage taken. In