Generally if it takes 3 tumours to connect to a base it would be considered to be a 4th or even 5th, that's not to say you need a choice of 3rd on 2 players maps but on a 4 player it's more important that you can expand in either direction. and just to prove my point here's a list of maps where your thirds are connected by 2 tumours:
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Year Zero (2), Kairos Junction (2), Automaton (2), Port Aleksander (2), Cyber forest(2), New Repugnancy(2), Stasis (1), King's cove (2 but the creep just barely touches if placed the tumor is placed in the right spot for 1 base), Blueshift (2), Fracture (2), Para Site (3 bases), and to name a 4 player map Darkness Sanctuary (2)
if it takes 3 tumours to get to either of your bases zerg gets screwed because it's harder for them to defend drops or aggression, and depending on spawn positions it can be amplified by the fact it's a 4 spawn map, not only that, it's far enough that it makes it hard for protoss to take a third safely.
Having some areas be chokier and others wide open is fine, but your center is just a wide open space with a small hole in the middle where anything daring to travel up there looks like it would just get surrounded by lings and because of the size of the middle it looks like it just shoves everything else out and the main looks like it does that same making the area you have in between very cramped. and if you break down the rocks you basically have 1 direct path to the opponent which I don't think is interesting.
I'm not sure how much the watchtowers will deter drops especially since the most direct route can completely avoid it and the bases are close by air with a lot area covered by the base i think the inhibitor zones would probably do a better job of that.