'Functional training' isn't automatically better than classic lifts
'Functional training' — exercises mimicking everyday or sport-specific movements, often on unstable surfaces or with unconventional equipment — gets marketed as a more 'real' alternative to classic strength exercises like barbell squats or bench press. The logic is that these exercises carry over better to real life and sport.
The problem is that 'functional' is a vague term: scientifically, any exercise that improves a specific quality (strength, coordination, stability) is functional for that purpose. Studies comparing training on unstable surfaces to classic exercises on stable ground more often find that the classic versions produce bigger gains in strength and power for the same effort — because a stable base lets you use more weight and load the target muscles more fully instead of spending effort just staying balanced.
That doesn't mean balance work and unstable-surface training are useless — they make sense for specific goals like injury rehab or sport-specific prep where balance is genuinely critical. But as a replacement for basic strength exercises for most goals — building strength and size — they're usually less effective than their 'non-functional' classic counterparts.