I would have loved to see an upgrade of Wanamaker and/or the addition of another shooter. The bench is simply not a strength right now and even with the starters playing increased minutes, it doesn't necessarily make bench depth meaningless in what is hopefully a long playoff run. Just because last season we had some selfish veterans (Marcus Morris worrying about his next deal comes to mind) doesn't mean that there aren't vets out there who are fine with a complementary role.
Even if the buyout market didn't exactly produce a lot of great difference-makers, the fact remains that what we have now is really lacking in offense. Whether that means the team should have been better constructed in the offseason or before the trade deadline, we can't say for sure because we don't exactly know what was available.
I really believe the general plan before the season started was to take a slight step back from "win now" and give Tatum and Brown the full minutes they needed to develop and see what happens. The fact that Tatum has improved so quickly, I think, is a little surprising to the FO because now the team is looking like a borderline contender. Now, I don't think Tatum is necessarily going to be avg'g 30ppg in the playoffs, but he's shown he has the ability to explode against the top teams and I just don't think they thought he'd be doing that until maybe 1-2 years down the line.
Unfortunately, they just didn't have great roster flexibility in terms of tradeable contracts. Considering how much they like their class of 2019, I know they are not eager to use all three of their 2020 first rounders, so I don't think holding onto picks was the issue (especially considering that the 2020 draft is supposed to be weak). Their only tradeable deals are guys they still want to hold onto, so there wouldn't have been a great net gain in a potential trade. If they traded one of the kids, their contracts are so low it would have made contract matching tough.
All in all, I can see all the reasons they didn't or couldn't make a deal for bench depth. However, it's just a shame because this team is playing really well in a season where there is no real overwhelming favorite for the title.