1) If you pay $10M a year in FA, you're never going to win anything, those values are ex post based on teams that ended up with the "winner's curse" - and one reason offers have drastically declined the last two years - teams are now basing offers on expected value, not unbridled optimism, and I'd say ex ante prices are $7-8M per expected WAR.
2) There's not a lot of cheap WARs, the first couple years, most players are close to 0 WAR, for every Trout, there's a dozen Kingery's. By year three salaries start creeping up, and by 4-6 you're probably paying $4-6M a WAR. If you need 40 WAR, you have to average $5M a WAR, try that with 15 WAR at $10M.
3) Alfaro is not a good bet to improve, because he's not fundamentally sound as a hitter or defender, and he turns 26 this summer - at some point he is what he is, and for all we know, he'll be similar to Rupp, who put up .750 OPS at 27 and .716 at 28, or Joseph, .813 at 24 and ,721 at 25, offensively. Alfaro's tools will keep him in baseball longer, but he's got the same issues those two did, power without a clue. Pitchers watch film and attack their weaknesses.
4) Sanchez is high ceiling and high risk, which is a limited expected value. I'd bet on Howard, who is very inexperienced at 22 (23 in July), but has a much better body (6'3 205) for a high velocity pitcher and has made real strides in developing secondary pitches. Had Sanchez stayed healthy and started on a regular basis he'd be much further along, but 3 seasons, 217 total innings. It's not just durability, it's a lack of progress, even great stuff needs one or two 26 start seasons to develop a feel for pitching. Howard is also inexperienced, 37 IP at 19, 12 starts at 20 in college and 9 more in Williamsport for 115 IP, 23 starts last year (112 IP). This year they'll probably stretch him out and let him go 5-6 IP per start. He may beat Sanchez to the majors.
It's great to have a lot of high ceiling pitchers in the minors, but minor league pitchers never win major league games. So there's always a balance between win now, win later and win never. Realmuto should get a substantial CBP jump, He wasn't cheap, but the price wasn't unreasonable. We do have three kids in the majors throwing 95, and De Los Santos in AAA - so it wasn't like Sanchez was the key to the pitching staff the next couple years.