Svi to me was a hedge----the strategy was to go 5-out and have depth of shooting available. If they had a significant injury to a wing or guard, or if PP slid defensively and had to be played more situationally, Svi was part of the response to that to keep the offensive scheme in place.
Those things didn't happen, fortunately.
Tillman, to me, was primarily brought in to provide a widebody for three specific possible matchups---GA, Embiid, and Jokic. And secondarily to improve big depth, and tertiary to see if he mgiht be part of the bigs rotation going fowrard. The first of those didn't happen; the second, though, came to matter as KP was hurt and while Tillman didn't play a lot, he had some key contributions in Dallas series which matter. And third is still TBD.
You build a roster for a bunch of scenarios that may develop and it's ok if you use some cap space or 2nd roun dpicks to prepare for scenarios that do not happen. For a contender, far better that than to be stuck playing Rasheed 35 mintues because you lack that one extra playable guy when you end up needing them...