I find it odd we haven’t embraced the modular spaceship and EOR approach.
Think of a Falcon 9 second stage but instead of payload, it had more tank, more fuel, a docking ring and a set of RCS thrusters. It gets to orbit, finds its ”passenger”, docks to it and pushes it into whatever trajectory it wants to go.
Add a truss with multiple docking rings to your payload and you can add multiple tugs to give a larger payload a bigger kick.
Even packing a few kick stages on top of F9s or F9 heavies would enable some interesting missions - as both trajectory can be higher energy and payload doesn’t need to be trimmed to the minimum viable mass.
Delta-V is more constrained by available fuel than number of tugs. An in-orbit refueled SpaceX Starship (or a fleet of them) will likely handle all the requirements we are able to manufacture for, in the near future.
Think of a Falcon 9 second stage but instead of payload, it had more tank, more fuel, a docking ring and a set of RCS thrusters. It gets to orbit, finds its ”passenger”, docks to it and pushes it into whatever trajectory it wants to go.
Add a truss with multiple docking rings to your payload and you can add multiple tugs to give a larger payload a bigger kick.
Even packing a few kick stages on top of F9s or F9 heavies would enable some interesting missions - as both trajectory can be higher energy and payload doesn’t need to be trimmed to the minimum viable mass.