I'm not going to argue in favour of the XBOX branding, I was just explaining it.
As for Avast not being removed... it's probably specifically marked as Win10 compatible. S&D may be compatible but not marked, or you may have had an incompatible version installed and have installed an updated version after upgrading without realising. As for replacing Avast - I personally think Windows Defender (the AV built-in to Win 8+) is fantastic, especially with OS-wide smartscreen enabled (warns if an executable isn't recognised by the AV, rather than just guessing it's fine like other AVs). Microsoft's database is nonsense-huge.
I don't recall if VGA advertises specific resolutions or just max H/V frequencies. If the latter, it's possible your monitor inadvertently advertises support for a resolution it doesn't actually support due to it falling within the required frequency limits. I do know Windows 10 tries to use the highest advertised resolution by default, to avoid a poor experience for non-techies upgrading and ending up with their display looking like shit until they change it manually (which they won't know how to do). Letting the user decide... hahaha! Have you met normal users?
Windows 10 doesn't demand DVI (it actually has no idea about the cable), I was just saying VGA is shit. Which it is. Issues like this are not uncommon with VGA, nothing to do with Windows 10. DVI is actually out-dated also, the current standards are HDMI and DisplayPort. Unlike DVI, neither of those can be converted to VGA with a passive adapter. Analogue video cables are dead dude. You shouldn't be surprised that there are issues with compatibility with a brand-new OS.
1600x900 is a perfectly common resolution, a load of laptops have it and there were even some desktop TFTs made to that before 1080p became so damn common. The steam hardware survey lists 6.63% of steam users as using that resolution.