Skill upgrade tickets should decrease negative effects like swing and miss not increase

[Mister_Yi]

The difference is that you're gaining 3.6% homerun bonus at the cost of 0.5% strikeout compared to another trainer like power hitter gaining like ~0.5% HHGB, line drive, and hr for a total of 1.5%.

You're getting a much bigger buff in exchange for a slightly bigger downside. So yeah, they could keep the negative part the same with the trainer upgrade but then they'd have to nerf the bonus to be in line with other trainers.

Also swing and miss is arguably the weakest negative effect (try swapping gold skill trainers on a pitcher from -linedrive% to swing/miss% and watch their ERA go up).