Agreed, I think the constraints built into Codex’s game design that my various variant ideas seek to circumvent were put into place for good reason, to keep the possibilities manageable (especially to avoid overwhelming newer players who already have a big learning curve in just becoming aware of what the cards in their opponent’s codex are capable of).
That specific combo was one of the motivations for my Variant Rules Proposal: Custom Starter Decks, and I can confirm that even that degree of expanded freedom significantly increased the difficulty of play, both because a big part of learning Codex strategy is becoming familiar with the standard starting decks’ capabilities and how to play around them, and because designing a starter deck that is flexible enough to be viable against any possible starting deck your opponent might think of is quite a challenge.
In part, this proposal is an attempt to allow those multi-starter combos, while being less overwhelming, as I expect players to have some general strategy in mind to work towards going into a game and to primarily focusing on advancing that strategy initially but then adapt to their opponent’s choices as the game progresses.