This disparity doesn't seem at all in line with the real-life applicability of having a high intelligence.
I'm thinking of offering, in the campaigns I run, intelligence as an alternative to dexterity for initiative rolls, such that players can choose which modifier they'd like to use. It seems obvious that being extraordinarily brilliant would give one a leg up in terms of one's reaction time, and I don't really see any drawbacks to allowing it as an alternative to players. Can you?
I do something along these lines. Inspired by the AD&D initiative rules and the Speed Factor variant from the 5E DMG, I do this every round:
1.) Declare actions, in order from least intelligent creatures to most intelligent creatures. (I.e. quicker thinkers can decide what to do at the last minute, even after they see what everyone else is doing.)
2.) Roll initiative, using DX modifiers as usual, to see who actually
completes their action first.
3.) Resolve actions.
In practice, step #2 can usually be skipped. Recently, the only time I actually
roll initiative is when step #2 turns out to matter, e.g. "did the drider get his shot off to hit the monk before the barbarian killed him with his 33-HP critical?" But if the drider didn't die, then it just wouldn't matter whether the drider did his 12 HP damage before taking 33 HP of damage.
For the most part this is pretty clean and quick. The one place you have to be careful is to make sure everyone declares their action before announcing the results of their rolls, because the high-int guy shouldn't know whether everyone actually
hits their targets before deciding whether or not to Web--he should just be able to tell what they're
attempting to do.
One additional twist that I added recently: anyone can Hold their action, in which case they decide what to do after everyone else has already resolved their actions. It's not quite the same thing as Readying an action before you're not locked in to a specific action, but the downside is that you automatically lose initiative to everyone who didn't Hold.
I've been using this system for a little over a month now (4 sessions? 5?) and it is working out well. The fact that it gives a reason to not dump intelligence (unless you are playing a straightforward brute who always uses the same strategy) has been mentioned conversationally by my players, but without any apparent resentment, so it probably doesn't make Int overpowered.
