Ok here's what I'd like to say,
I absolutely hate the mine talents, mainly because they are worthless in the late game. The only good thing about global mines is that it can let you teleport wherever you want. It is only good if you are trying out the push build. But imo if you go for a full siege build your team is most likely going to lose every team fight because picking up all the push talent makes the hat weak. No bonus attack speed, no healing, no slows, etc. I only ever do the siege build when I feel that the symbiote is not gonna be of use in the game (comps with Hammer, kael, etcetra.).
In short if you are doing a push build your win rate is going to drastically drop since it SUCKS! A single Sylvanas can absolutely wreck your push with a singe W into E and picking up all the siege talents is never a good idea in the current state of Abathur.
Ultimate evolution is definitely on par with Monstrosity, it isn't a trade off, One thing we need to know is that Abathur is a support hero (his days of being a great lane wrecker are gone). If you want to push lanes then your team fighting abilities are hindered significantly. A well timed and well positioned clone can be an absolute beast, 20% ability power and 20% atk dmg is no joke. A good Abathur clone can completely change the tides of the team fight.
Hivemind is good even if you have an Illidan that constantly jumps in, I have played with friends and they know to stay in range of each other. Also if the second hat dc's i am usually constantly reapplying the hat anyways so it isn't a huge deal.
Compare Abathurs talent picking decisions to the other specialists. You have to choose between pushing or team fighting. Picking up pushing talents is usually not the way to go and the same goes with Abathur.
TL;DR Don't favor the siege talents, Abathur is a better support post nerfs. Ultimate evo and Monstrosity have their own place. Mine talents suck since they are useless in the late game and pretty underwhelming. Hivemind is still better even if your team mates keep seperating since they will group up atleast once during fights specially if they are melee.