It doesn't really matter because Shane and Brad were always destined to be "one year only" players. Here is why:
Both were signed as non-drafted free agent rookies. Let's use Brad as an example: He will be a RFA after this season. The C's have 2 options to resign him to a minimum deal:
1 A 1 yr deal at the 2 - year vet min that would give Brad a no-trade clause (C's do not want to be
locked into a no trade provision with anyone at the end of the bench)
or
2 A multi year deal at the 4 - year vet min (This might be too expensive for C's given their luxury tax
status)
It was the same 2 options in summer of 2018 with respect to re-signing Shane or not. This is why C's didn't bring Shane Larkin back - it is cheaper and more flexible for C's to just to bring in someone new each year from Euro leagues.
The team has an interest in building relationships with agents and players; and there's positive value in cultivating European connections. So despite the transient nature of these contracts, they are part of the long-term success of the franchise.
If C's keep all 4 of their potential first round picks in summer of 2019, it may not even be necessary to tap back into the Euro league market this summer.
The role of either Larkin or Wanamaker is "Break Glass in Case of Emergency" third-string point guard. What they want at that position, in other words, is someone with experience who can run an offense. That's different from the developmental slots that rookies would likely be in, precocious children like Tatum and Brown notwithstanding.
It's unlikely that Boston keeps two draft picks, let alone four.
Getting back to OP's question: I prefer 6 ft 4 in Brad. I have a real problem with players under 6 ft 2 in playing on my team in NBA: just too easy for other teams to create mismatches with a really short player. The plan is for all the Celtic guards to stay relatively healthy and therefore have Brad play very limited minutes. Brad has played very little and I am more than OK with that - hot dog everything is going to plan! (so far).
I agree. Though Brad doesn't have Larkin's fifth gear, you wonder if signing him is the Celtics Brass' reaction to watching Larkin get overpowered on D. Wanamaker has a beautiful stroke, too...