Not sure of your definition of a “really good team” is, but I believe 3 of the division winners last year — Yankees, Phillies and Brewers — didn’t have a third baseman hit 20+ home runs (minimum). Actually either did the Dodgers, but that is because Muncy was hurt. Not sure if any of those teams got 20+ HRs out of the position cumulatively (guessing Dodgers did at least).
Sure third base is traditionally a power position, but plenty of ways to assemble a team. Heck, while the guy everyone wanted meets your HR minimum requirement, Bregman isn’t near the traditional big power hitting 3B. Outside of two early seasons of 31 and 41 HRs, he’s only averaged 25 in the 3 full seasons he’s had since then.
I’m not sure what you mean by given up TWO third basemen. Do you mean Paredes and Cam Smith? Very few fans if any had qualms about giving up Paredes and based on his time as a Cub, he likely wouldn’t have hit your 20+ HR minimum. And he’s not an above average glove. Smith had a real nice spring, but isn’t exactly burning things up. Yes, he’s doing better than Shaw did.
Cubs gave up some decent players, one of which might end up being more than that. Would you rather have Hoyer not made the trade? Cubs would likely be mediocre at best without Tucker. Yes, we need Cubs to sign him, but after seeing his impact on this team I’ve come around to believing the trade was worth it even if they don’t re-sign him. To win, you need difference makers. Tucker is one and none of the players Cubs gave up to get him are. Smith might be one in the future, but we’re not talking about a can’t miss star in him. Would you have rather Cubs didn’t give up Gleyber Torres for less than a season of Aroldis Chapman — and a World Series championship? Torres was a top 25 overall prospect. Smith was outside top 50.
Third base is absolutely a problem. Hopefully, they can plug the hole. Maybe Shaw is able to help in second half of season. Maybe they trade for someone sooner than later. But I think they should have have made the Tucker trade whether they re-sign him or not. And while I’m not pro-Hoyer, him not re-signing Tucker is not grounds for firing him — that is on ownership. One can find plenty of other reasons to fire him, but I don’t put making the Tucker trade or not re-signing him should they not to do so on the list.