You could try a different browser but just know that every browser on the Apple store uses the same rendering engine(Safari) under the hood. This is by design, Apple's ecosystem is very tight and locked down. Chrome and Firefox are basically just Safari with a different skin as far as rendering goes. That doesn't mean they don't do anything differently at all though so it could be worth a try.
On March 12th 2019 it looks like QuickBase had an iOS and Android release specifically for tablets. Before this I believe they didn't really fully support tablets. Have you tried the app since then? It may have a better experience than you had before. It is something worth checking anyway.
Other than that I agree that any time you spend on improving mobile forms would be well spent. You might have to re-create many forms but if you have a lot of mobile users it should pay off big time if you can make a much better user experience.