I disagree with this but would like if characters were able to upgrade the limited fortifications they’re able to build. This would increase viability of teams lacking an engineer.
One of the primary roles Jack can undertake is assistant-engineer, repairing and moving fortifications more efficiently than anyone having to buy a repair tool. There’s nothing wrong with others helping move/repair things if required but they don’t need buffs in that regard unless it’s in the form of a skill card they need to equip.
Del really shouldn’t be spending much time killing anything once you’re well into a match. He has some cool combat-related cards that would be fun, but using them would detract from his utility. I guess the exception here is sentry-light, heavy weapons-focused games.
It is nice to have support as an engineer though. I played as Del with a Jack and Kat and thought the overlap in shared roles would cripple the team. It was the opposite. We had a sick base and time to do some shooting.

Del flat out gets better cards, no denying that. I’ve been in games with Kat an Del and lets just say no sentry was empty, no fence was near destroyed(before the 3 barrier glitch) Del built things at first but after his cost went up then Kat would start building.