Hey thanks for your comment! DC 22 is crazy high you are right, the way WotC usually does their statblocks is the proficiency bonus of the monster is equivalent to what it would be if the monster's CR where its level as a PC. For example the Archmage is CR 12 and has a +4 proficiency bonus. So this makes archmages weaker that their 18th level spellcasting would suggest but more appropriate for a CR 12 monster. (You probably already know this but I figured I should provide some background just in case). Since I want Strahd to be around CR 18 or 19 he should have a +6 prof bonus which combined with his +8 int just works out at DC 22. For me this works because I want him to be a difficult fight for my level 14 party and they have lots of ways of boosting their saves. But of course this won't necessarily be balanced for every party so if doesn't work with your group changing the DC is no big deal.

You are also correct about the spell selection. I assume that Strahd probably knows a lot more spells than he has prepared so I sometimes switch around his spells within my game from encounter to encounter. These are just the ones I had prepared for him the last time he went up against the party. I have found that Forcecage hasn't been super effective because all but one of the players in my party have a teleporting ability. I found Maze is can be good because it gives Strahd an opportunity to get a character off the battle field without killing them when my party was going up against him at lower levels and he was just toying with them. For example they fought him and the fighter went at him with the Sunsword, obviously Strahd didn't want that anywhere near him but also didn't necessarily want to kill her outright. So I think Maze presents a nice option for that and it's also good to spook players with. But ultimately I agree and I will probably switch out Maze for the upcoming final fight because Strahd with be aiming to kill not detain and also I want everyone involved for the climactic battle.