Which is what happened since the move to Unity. Players favor a platform because major gameplay differences. PC for PvP because of speed animation and Mobile for GWs because AI and cascades is "tamer".
Agreed with OP that surge in 4 matches makes a huge difference in gameplay. I'm not saying 4 matches should never surge. When my guildmate post a board picture asking for help, I always ask them if they play on mobile or PC because that will determine my decision to perform certain move e.g. whether to match 3 or 4.
Speed animation also makes huge difference in trophy/PvP points gained. There's no way players who play only in mobile could compete with PC players on the leader board. Another thing I concerned about this speed thing, and I've questioned it before it goes live, is if you guys could differentiate when someone activate it or using bots/3rd party program. Because you guys have problem to detect some of those programs or bots in the past.
So until all using the Unity version, according to your post, consider disable some features that's not available on one platform until all using same Unity version.