For me, my biggest issue with Siege is the cannons. I've mentioned it before but I recall being summarily dismissed. I think they are far too effective as base razing due to where they're positioned, seeing as only infantry or artillery can damage it in any way. It feels cheap seeing as you probably already have lost control of mid for the enemy team to get that far forward. If you haven't already lost mid, you'll probably lose itas a consequence since you either need to hang back to repair; grab an arty unit and hanging back to snipe it, but also at immediate un-dodge-able of being 1-hit killed by the cannon yourself; or use inf to get up to it, but pray that you won't be pummelled by the vehicles holding mid as you try to get to and run up the slopes to reach the cannon.
That's my feeling of Siege anyway (Hello me @Fegman891 in the logs).