I'd like to see the games spread out over a greater number of guys - looking at the 2018 AL leaders in appearances: Pressly was #1 with 77; Hildenberger was 7th with 73; Zach Duke was tied for 10th with 72 along with Taylor Rogers; Even Rodney hits 21st with 68.
That 4 of your relievers, (albeit some of those appearances were with other teams) make the top 10 league-wide in appearances, no bueno. The only team that had more than 1 was Seattle, and one of theirs was Duke.
No more LOOGY/ROOGY Rule 5 passengers in the bullpen....
I believe a couple of factors came into play to produce the results you mention.
#1 - Health - We had a couple of DL stints but for the most part, our pitching staff remained healthy and when healthy they will rack up the innings in comparison to other teams in the league who are enduring injuries in a more typical amount.
#2 - Hiding and Burning Roster Spots - We started with 7 bullpen slots and the hiding/burning started right away when the Twins selected Tyler Kinley in the Rule 5. I had no idea who Tyler Kinley was but the idea of selecting a Rule 5 guy while at the same time spending money to sign free agents seemed contradictory to me. Selecting a rule 5 guy and returning him shortly after may seem like a "Oh Well We Tried" harmless spin of the wheel for a short time but Molitor wouldn't use him and this ratchets up the number of appearances his trusted bullpen posse would need to compensate for. Kinley made 4 appearances in April before he was returned to the Marlins on May 1.
After Kinley was returned to the Marlins, Phil Hughes was taken out of the rotation around the same time and Hughes replaced Kinley in that long relief role and went on to make 5 appearances out of the bullpen until he was traded to the Padres May 27th. That's basically two months of the season and 9 appearances total between Kinley and Hughes.
After Hughes was traded... Molitor... seemed to have a "we have to have someone held back) for long relief desire or need. That guy then became Matt Magill. After making 12 appearances in May and an impressive 1.53 ERA. Molitor had to have someone replace Kinley and Hughes and not pitch much in case things got bad in a game and Magill disappears of the radar for a total of 5 appearances in June. Now we are at 14 Appearances out of the long relief role for the first 3 months.
This created a domino effect in the bullpen. When Magill switched roles, as mentioned above he went from 12 appearances in a month to 5. This means that someone would have to be added to roster to replace those innings that Magill used to absorb. This becomes a line of candidates who Molitor didn't seem to trust much and they don't replace the appearances that were being made by Magill. So now we are using up two bullpen roster spots to hide and basically waste and the trusted posse who remained healthy has to take up the slack.
In my opinion... it was the combination of these two things that created the impressive list of Twins pitchers at the top of the MLB appearance rankings.
I don't know if I've mentioned this before in other posts but in case I haven't. -- In 2019... I want 25 guys who can play and every player on the 25 man to be trusted and utilized.