Hi, everyone.
There's a little bit of "dillemma" and I just try to ask how YOU would deal with that situation. A "who to choose for 5th spot" dilemma

Have some time before return to the game due to much of workings.
There is a fictional league, started 1901 (now end of 1914 season). I'm playing with a mid-market team (based in Milwaukee). Classic 16 teams divided into two leagues with winners playing in WS. Reached WS 7 times, 6 times won, including first ever sweep this season.
My 14-year pro strating catcher retired after this season in which he served PH-role largely because of NO-defense. New starting catcher (7-year pro, 1st as starter) proved to be elite defensive catcher (close-to-60% caught stealing, +30 zone rating, 1.100 EFF, around 2.00 CERA) with no bat (.210 last season - worst among starters). As I found out, good catching (and overall good defense) is a short way to success in my fictional league, so this guy will remain starter for 1915, but this is not dilemma. It is in pitching.
I have 13-year pro (all in my team), 34-year old player, career 185-game winner, 1902 ROTY, 1300 Ks (2nd in team history) and around 2.50 career ERA. He's wrecked, though lucky in injuries lately, working 25+ starts in 3 of his last 4 seasons. Never been an ace, mostly 3-4th starter. Fair popularity. I rejected team option for him, thus he should be a free agent month later, asking 5000. My highest paid player earn 14000, with average arbitration contract between 1500 and 2000. Last season he's 14-9 with 2.76 ERA and rough finish (25+ ER in final 5 starts). Still he's a reliable starter who improved since his early seasons (in first 5 years he averaged below 95 ERA+, while in his last 5 years averaging over 110 ERA+). His ratings as scouted by team scout sit at 7/15/15 (stuff/movement/control) with 3 pitches rated at 10-11 (1-20 scouting system). He's 3.5 stars overall.
And he has a competition for final spot for the next season. Competition from 22-year old rookie, who pitched 12 starts this season in Majors with 10-1 record and 1.76 ERA. In Minors he was 10-8 with 2.23 ERA (2nd best in team behind guy who was traded in deadline for some outfield prospects). In Majors he won Rookie of the Month award, but had an issue with his command issuing more walks that Ks. He pitched 2 shootouts in final 3 starts in September including a 1-hitter. Had a battle for NL pennant until final week. His ratings 7/11/9 with 3 pitches rated at 9-10 with little upside (by team scout) and normal work ethic and intelligence. Overall at 1 star. He's only for two seasons in my system after being acquired in trade, but pitched amazing through AA and AAA in those 2 years with combined ERA around 2.00. And he's durable.
That is a dilemma. With superb defensive catcher, pitcher coach rated LEGENDARY in pitching and at least Outstanding in handling rookies and veterans, GM rated at least Outstanding in those categories and overall well above-average defense (though biggest holes are on 2B and CF with average to below-average, but 2 of 3 team best hitters including ML-record holder for RBI's in a season and defending ML RBI champion, 3rd in batting race and one of the league-best leadoff hitters - FA asking 10000+, would be signed) I have a big question who to use.
I can sign veteran and then trade him away for some prospect. Or keep him in lineup and promote youngster in case of injury (2 wrecked pitchers in rotation, 1 of them missed 8 months combined during last two seasons and is 38-year old - he's rated 9/17/20 though for 5 stars). Or avoid signing veteran and promote rookie to 5th spot. Still have 5 pitchers in Top-100 Prospect list, though mostly at 50-70 numbers. And about 130 000 for extensions, which indicates that signing is not a problem.
What way would you prefer??