Now you hit on the sole point in favor of your arugment.
We have more legislatures right now so we could have more Senators than we currently do.
We also wouldn’t have controlled the Senate from the 30’s until this century.
Not to mention hundreds of millions of dollars now spent on Senate races would instead flow to those state leg races and effect the outcome.
Short term, theoretical partisan advantage is to me, certainly not enough. If it looks like the GOP will have permanent state leg dominance the argument becomes stronger.
"We have more legislatures right now so we could have more Senators than we currently do."
Ideology was a little blurry in a lot of ways. You had Blue-Yellow dogs. You had "liberal" Republicans and "Conservative" democrats. Lines are clearer now which is why Repubs control a large percentage of State Legislatures.
Fiscal policy (Including under so called "Conservative" control) has been embarrassing since voting rights expanded and populism emerged (Electoral College is be targeted again). Frankly all your arguments are moot points based on this fact. Founders instilled gridlock on purpose and understood the power of "factions", thus restricted the process away form "Democracy" and more into Representation through multiple tiers to make the process slow as possible.