I think this FO puts a very low priority on relievers even as prospects, and I get the logic on that compared to every other position, but we've also been paying the price for that. They trade or waive them like candy.
As it stands we only have 1 seemingly effective above-average reliever and possibly 2 if Merryweather is back and effective which are both question marks. We probably have 1 or 2 effective SP who can also go to the pen. Brown is a late-inning guy if needed but could be our best #5 SP option. You can fill the bottom half of a pen with JAGs no problem but we still need to figure out the 8th inning and have some depth in case of inevitable injuries.
You're right that building a pen in FA isn't the best strategy, you end up overpaying a lot for guys who are genuinely good. And guys like Fulmer, Boxberger were just average relievers when signed, basically JAGs not really worth investing millions on. Neris was a slightly above-average reliever at best and well into age-regression years, no idea why they signed him to that deal unless they thought a career year at age 34 was legit even though the xFIP was pedestrian.