I've had both 45g and 55g RF keyboards. My preference is 55g Topres; however, there are a lot of people who love the feel of and prefer 45g to 55g RF KBs. After typing much of the day on my 55g keyboard, I'll go to my MX Red keyboard for a lighter feel; but if I had a 45g RF, I'd use it at day's end rather than the MX Red KB. My digits get a bit fatigued after a full day on my 55g RF. Nonetheless, it's my #1 Topre switch.
Topre's 55g switch is not at all mushy; it has a definitive feel but the switch is, how should I say this?, firmly buttery. I can feel the resistance, but for me it's good. I tried an HHKB a short while ago; and in comparison, RF's 45g feels less firm than the same switch on an HHKB. It's still mushy, but I found a Topre 45g on an HHKB has a slightly firmer feel than the same switch on a Realforce 45g keyboard. Just one guy's opinion.