I agree with corsa in that there are definitely different ways to practice and it kind of depends on your team and the team you're scrimming against as to which is 'best'. If, for example, you scrim one team a lot and learn that they like to play super aggressive, you may find that your passive mid is a good counter to them. If they keep bombing in aggressively and you are able to clean them up effectively, then it could be argued that you shouldn't change anything. After all, it is still good practice and will make you better at executing the passive middle in the future. However, you definitely don't want to entirely rely on that one strategy especially given the fact that most of the time you don't scrim the team you play in an official match on a given week (at least in NA usually), because for all you know it could completely back fire in the match and cause you to lose middle.
No matter what you do in scrims though what ultimately matters most is you are flexible when it comes to match settings and are able to adapt to what the other team is doing. You can play with this in mind during scrims or just dedicate one scrim to practicing a given middle, regardless of what the other team is doing. Even if going your side seem to be working on gullywash in scrims, it's probably useful to switch it up and practice going big door/their side just so that in the match it's not your very first time doing it.
If you are losing mid and keep doing the same mid multiple times in a row without changing anything, and expect different results you're an idiot. (shoutout to bullet for rolling out choke every mid on gullywash vs strolling astronomers and expecting not to get locked out by yuice & friends who went our side every mid, weapons grade autism right there)