Using a club and a second weapon (third attack) with Warmagic and Shillelagh and Hex will outdamage using a staff by quite a bit, even without knocking enemies prone. You are getting the same attack damage as you get with a staff and then getting one more attack on top of that.
I think you are forgetting that you have Hex in this build. Finally you can go dual wielder at level 8 and get a 4th attack as a bonus action with your shillelagh club. That would be 3 Shillelaghs plus a scimitar. This does get bonus action starved, but I think it will outdamage all the other builds both in the white room and in play.
I would agree that slow is not that great, but you can get stuff on your missile weapons - get nick with a dagger and push with a Heavy Crossbow in addition to your nick scimitar and you are pretty darn good at ranged attacks too. Later on add SAP from a spear.
If you are really dead set on topple, grab a Trident and start out by using it and toppling with Truestrike and then switching to your Shillelagh Club-Scimitar combo for your 2nd and 3rd (and 4th?) attack.
A club with shillelagh and a nick Scimitar is going to outdamage a Vex-nick build.
I mean a Shillelagh is 1d10 at 5th level and uses Wisdom on both attacks you make with it, a short sword or hand axe is 1d6 and doesn't use Wisdom for the attack. Vex on 1 or 2 attacks does not make up for that IMO.
Consider Starry Wisp too. You can't use it with Warmagic but it is great at making invisible enemies NOT invisible.
If you are taking a combat cantrip I like Balde Ward over Mind Sliver for using with War Magic, especially on a sword and board build.
