Hmmm , let's put it this way, if you were playing golf and you were on the first tee, would you drive off the round with a putter and play all the holes with the same putter
Its after all a golf club so what difference would it make using the one putter all day say compared to using the right club for the right job
Anyone answering that one correctly will also know the answer to using a purpose designed rod for the right purpose
My 3.5lb rods referred to above happen to also e Dave lumbs rods, baitblasters, also referenced by another poster and they're superb rods for piking and the one thing that I will say is that I never experience reeling in dead weights
Its alo true you can compromise a touch when choosing a rod to float fish with as you can use 2.5lb rods with a through action as you tend to fish close or near bank anyway, the key though is a proper through action so you don't rip the baits off on the cast or lock the rod up when attempting a cast
My lad when he was younger used my wychwood 1.75lb barble rods for close in piking, they matched the strength he had a a nipper to the rods power and he was able to get a bend in the blank and use the rods power but they are wychwood rapier rods and pretty good blanks (allegedly greys blanks from the same Chinese factory) but S he got older and stronger the tc's of the rods he used gradually increased in relative terms to his strength
Indecently his best pike on barble rods was 17.5lb on nearside float tactics
My advice would be to buy a decent rod with a tc of at least 2.5lb with a good through action and the best you can afford as circumstances allow, you won't regret it, as a previous poster has already said, the difference in fishing with a make do rod and one designed for purpose is like chalk and cheese