Having played it, there is definitely things that needs to be improved.
This is a gamemode that would benefit very much from very large maps. The reason for this, is so there can be longer distance between the capture points, so the defenders will have time to set up defensive positions. Because currently, the way the defenders are able to set up a defensive formation, is but sacrificing a capture point. If they die, then most of the time not able to get back to the capture point they need to defend, since their spawn is very far away from the capture point.
I would also highly suggest you take a look and use/take inspiration some of the mechanics from Battlefield 1 Breakthrough game mode. Key features that I feel the Advance gamemode could benefit from, would be that there is 2 capture points that needs to be held at the same time, and that defenders can recapture. Another is that when attackers have captured the points and are able to advance, there is a grace period where attackers are not able to advance, so defenders have time to set up defensive positions, so it doesn’t become a steam roll. This would work somewhat the same way as bigger maps would, with giving time for defenders to set up positions.
While i have not tried to play defender where we got to the final capture point, so i am not sure how the spawn are with those. From what I did see on Port Novorossiysk, for the second capture points, the defenders spawn on the opposite side of the bay, and have to cross very far in open sightlines, to be able to defend the capture point, and that is too far for the defenders to travel, to have any kind of chance to defend their capture points. Another problem is also the early game on that map, is that the defenders don’t have time to go to the capture points in time, before it is captured instantly.
A key thing, is that early in the game, the attackers should have a bigger advantage, where later game the defenders should have a bigger advantage. At the same time, both teams should have equal chance to get into advantageous position. But a way that defenders can get a bigger advantage in later game, can be done by letting the defenders spawn closer to the capture points in the later stages of the game.
Like the attackers should not be able to move past the defenders spawn, equally the defenders should also not be able to move past the attackers spawn, to make sure that they can’t just shoot the enemies in the back. This could be done by, after the attackers have captured a point, then 1-2 min after that, the zone that automatically spots enemies too close to spawn like in the regular gamemode, gets place on the map near the attackers spawn, with nearly everything behind that spawn.
Another thing is, that if you make some of the existing maps bigger, so that they can be used for this gamemode, they would probably also be able to used for the regular gamemodes, where there is some of the playerbase (me for example) that have been asking for larger maps. The thing is, even though a map can be large in regards to the area it takes up, it can still feel like a small map, if the sightlines that is there is not that long range.
Overall, it is a good gamemode with a lot of potential, but as it currently is, it is as they say a diamond in the rough.