Hi there, I just played your map's a10 version. I've played some earlier versions before. I'm not a mapmaker, so I'm speaking purely from the standpoint of someone who plays a fair bit of mvm.
I think the map is much better now with the smaller/tighter spaces than the earlier versions, which were really wide, open, and hard to play (mostly because the bots could shoot you easily, but you can't do the same). I think there are now some other things though that need a little work
1) It seems to me that there's way too much money in the a10 version, even before you get to waves 9 or 10. By wave 4 my pyro was basically fully upgraded. I think you can safely cut the amount of money by half and it'll still be easy enough.
2) We played to the last wave with basically four people - two engies, one heavy, one pyro. There was also a scout and sniper, but in terms of damage they didn't do much, and we rarely left the front cave. We had two sentries set up, as follows
http://steamcommunity.com/sharedfiles/filedetails/?id=158346321
http://steamcommunity.com/sharedfiles/filedetails/?id=158346287
And that, basically, took care of everything pretty much as soon as they spawn. There aren't enough bots to even destroy the sentries. We rarely died. Some waves, like wave 9, for example, felt way too easy - with one air blasting pyro who is fully upgraded in resistances, the scouts/soldiers didn't even make it halfway up the ramp.
3) The only time we had some trouble was in wave 10 when one of the bots slipped past us, and we started getting engies behind us. That was the only point at which we ran into some problems. It was more annoying than anything though, as the breaks between bots spawning was really long, so my time, as pyro, was spent hunting down engies. The rest of the team stayed to kill bots spawning. It wasn't challenging either, because of the aforementioned reasons
4) The jarate thrower isn't working - he just hangs around the engi that he spawned next to and just sits there.
Right now I think the mission is about intermediate in terms of difficulty. Regular advanced missions are harder than this. I believe it can be made more difficult with more bots that are harder to kill - steel gauntlets, for example, are a great way to push the bomb along, and so are demoknights. Having two tanks come out at the same time might also make things tougher - right now I notice only the left tank hole is used (or maybe I missed one or forgot). I think using giant medics can help you push the map out of the first room. Tanks + a lot of bots can also do that.
Also, in terms of the map layout, I wonder if you could make it so that the initial room is smaller - right now it's really huge, and the bots are pretty much at the mercy of the players. That's fine, if the bots are a lot harder to kill and come in larger numbers, but they aren't, so right now I think the map is too easy for those who play a decent amount of mvm. Maybe reduce the amount of health/ammo in that room, decrease the length of the first room, and also perhaps allow bots to come out of the tank holes during non-tank waves. Right now since it's possible to just defend one point, it becomes quite simple to do.